Hello,

Does anyone know what this annoying clicking noise is?

It obviously has nothing to do with the air or ac cause happens all the time even when switched off.

please advise

Do know where it is coming from?

Is it when you turn the steering?

Does the car have to be moving for the noise to appear?

Does not sound good - needs investigating.

Sounds like from behind the speedometer

Not noticed had anything to do with steering

4 minutes ago, Spacewagon52 said:

Do know where it is coming from?

Is it when you turn the steering?

Does the car have to be moving for the noise to appear?

Does not sound good - needs investigating.

1 hour ago, b4u2 said:

It obviously has nothing to do with the air or ac cause happens all the time even when switched off.

The air con may be off, but the ventilation system is still operating. I would start by trying the ventilation system in different settings.

Just now, Spock66 said:

The air con may be off, but the ventilation system is still operating. I would start by trying the ventilation system in different settings.

I have played around with it but always still seems to happen

At what speeds do you notice it?

When does it happen? (i.e. first 2 mins from cold start, or irrespective of how warmed up the car is?)

If you find a long straight road and give little to no steering input, does it still happen?

Does it ever happen on engine idle? If so, can you see/hear anything unusual under the bonnet?

Doesn't sound good though so definitely needs looking into.

13 hours ago, LexusNelly said:

At what speeds do you notice it?

When does it happen? (i.e. first 2 mins from cold start, or irrespective of how warmed up the car is?)

If you find a long straight road and give little to no steering input, does it still happen?

Does it ever happen on engine idle? If so, can you see/hear anything unusual under the bonnet?

Doesn't sound good though so definitely needs looking into.

Not at a specific speed

Happens randomly

Yes it has happened on idle engine too

On 4/19/2026 at 12:29 PM, b4u2 said:

Hello,

Does anyone know what this annoying clicking noise is?

It obviously has nothing to do with the air or ac cause happens all the time even when switched off.

please advise

That rapid, rhythmic clicking or "tapping" sound coming from behind the dashboard/steering wheel area is a very common issue in Lexus and Toyota vehicles of this era (it looks like a third-generation RX).

The most likely culprit is a failing HVAC Blend Door Actuator (also known as a Servo Motor).

Why it makes that sound:

Inside your dashboard, there are several small electric motors (servos) that open and close flaps to control where the air goes and what temperature it is. Over time, the plastic gears inside these motors wear out or the internal tracks get dirty.

• The "Hunting" Effect: The car's computer is trying to move a flap to a specific position, but because the gears are slipping or the sensor is faulty, it keeps overshooting and trying to correct itself. This creates that rapid clicking or "ratcheting" sound.

• Why it's random: It often happens when the climate control system is set to "Auto," as the car constantly adjusts the flaps to maintain the temperature. It might also happen for a few seconds right after you start the car or turn it off.

---

How to diagnose it yourself:

1. Change the Airflow: With the engine on and the clicking happening, manually change the air direction (e.g., from "Face" to "Feet").

2. Adjust Temperature: Change the temperature from "LO" to "HI."

3. Check Recirculation: Toggle the "Recirculation" button on and off.

• If the sound changes speed, stops, or starts when you press one of these, you have confirmed it is a faulty servo.

---

What to do next:

• Is it dangerous? No. It’s annoying, but it won't affect the safety or drivability of the car. However, eventually, the motor will fail completely, and you might get stuck with only cold air, only hot air, or air only blowing from the defrost vents.

• The Fix: A mechanic will need to identify which specific servo is failing (there are usually 3 or 4 behind the dash). Some are easy to reach by removing the glovebox, while others are buried deeper.

• Temporary Workaround: Sometimes, setting the climate control to a manual setting (not "Auto") and finding a temperature/vent position where the noise stops can buy you some time.

3 hours ago, RXTakumi said:

That rapid, rhythmic clicking or "tapping" sound coming from behind the dashboard/steering wheel area is a very common issue in Lexus and Toyota vehicles of this era (it looks like a third-generation RX).

The most likely culprit is a failing HVAC Blend Door Actuator (also known as a Servo Motor).

Why it makes that sound:

Inside your dashboard, there are several small electric motors (servos) that open and close flaps to control where the air goes and what temperature it is. Over time, the plastic gears inside these motors wear out or the internal tracks get dirty.

• The "Hunting" Effect: The car's computer is trying to move a flap to a specific position, but because the gears are slipping or the sensor is faulty, it keeps overshooting and trying to correct itself. This creates that rapid clicking or "ratcheting" sound.

• Why it's random: It often happens when the climate control system is set to "Auto," as the car constantly adjusts the flaps to maintain the temperature. It might also happen for a few seconds right after you start the car or turn it off.

---

How to diagnose it yourself:

1. Change the Airflow: With the engine on and the clicking happening, manually change the air direction (e.g., from "Face" to "Feet").

2. Adjust Temperature: Change the temperature from "LO" to "HI."

3. Check Recirculation: Toggle the "Recirculation" button on and off.

• If the sound changes speed, stops, or starts when you press one of these, you have confirmed it is a faulty servo.

---

What to do next:

• Is it dangerous? No. It’s annoying, but it won't affect the safety or drivability of the car. However, eventually, the motor will fail completely, and you might get stuck with only cold air, only hot air, or air only blowing from the defrost vents.

• The Fix: A mechanic will need to identify which specific servo is failing (there are usually 3 or 4 behind the dash). Some are easy to reach by removing the glovebox, while others are buried deeper.

• Temporary Workaround: Sometimes, setting the climate control to a manual setting (not "Auto") and finding a temperature/vent position where the noise stops can buy you some time.

Thanks so much for your in depth response, however I can confirm that this noise happens even with the ac and fan completely off and when it's on, it's not on auto so obviously it must be something else wrong which is causing it....?

Even with the climate control off the car still let's air into the car and would it then still close and open potentially. Just a thought. But that noise sounds like a plastic gear trying to beyond it limit and jumping the cogs

11 hours ago, b4u2 said:

Thanks so much for your in depth response, however I can confirm that this noise happens even with the ac and fan completely off and when it's on, it's not on auto so obviously it must be something else wrong which is causing it....?

Good morning!

The vehicle still manages several systems in the background even if you have manually turned the "fan" or ventilation system off. Modern Lexus models are designed to be proactive about cabin air quality and component protection. Here is how the vehicle typically handles things behind the scenes:

1. Automatic Recirculation Control

Even if the system is off, the car may adjust the recirculation flap.

• The Reason: If the vehicle detects high levels of external pollutants (on models equipped with an exhaust gas sensor) or if the car is parked in high heat, it may close the vents to prevent outside air or odors from drifting in.

• The Logic: This is often tied to the "S-FLOW" energy-saving technology, which prioritizes air management based on where passengers are sitting.

2. Humidity and Fog Prevention

If the sensors detect that the windshield temperature and interior humidity are reaching a "dew point" (which causes fogging), the car may override your settings.

• The Action: You might hear a flap move or feel a slight draft. The car is positioning the vents to be ready for a defrost cycle or allowing a small amount of passive airflow to prevent moisture buildup.

3. Servo Motor "Home" Positions

When you turn the car off or shut down the HVAC system, the Lexus computer often cycles the servo motors (the little motors that move the internal doors).

• The Noise: You might hear clicking or whirring behind the dash. The car is "re-homing" the vents to a default position to prevent the seals from sticking or to prepare for the next startup.

4. Hybrid Battery Cooling (If applicable)

If you have an RX 450h, 500h, or 450h+, the vehicle has a separate cooling requirement for the hybrid battery.

• The Action: The battery usually has its own intake vents (often located under or beside the rear seats). Even if your cabin AC is off, the car may run fans to cool the battery pack if it gets too warm during driving or charging.

Air Flaps - May still move to block odours or prevent "sticking" of the seals.

Exhaust Gas Sensor - Remains Active to close the intake if it detects heavy smog/exhaust nearby.

Humidity Sensor - Remains Active to predict when the windshield might fog up.

Servo Motors - May cycle to calibrate the position of the blend doors.

Hope that makes sense 👍🏻

11 hours ago, b4u2 said:

Thanks so much for your in depth response, however I can confirm that this noise happens even with the ac and fan completely off and when it's on, it's not on auto so obviously it must be something else wrong which is causing it....?

11 hours ago, b4u2 said:

Thanks so much for your in depth response, however I can confirm that this noise happens even with the ac and fan completely off and when it's on, it's not on auto so obviously it must be something else wrong which is causing it....?

Please stop posting AI slop. It is not relevant to the OP's vehicle.

The RX400h isn't modern - it was launched 21 years ago.

It does not have automatic recirculation. It does not have S-Flow.

The video shows fogging / humidity isn't an issue

The cabin AC/ventilation system has no connection to the hybrid battery cooling system

Servo motor home positions - the system doesn't cycle servos to calibration them, it uses position sensors, plus any calibration would occur on startup, not when driving.

6 minutes ago, ColinBarber said:

Please stop posting AI slop. It is not relevant to the OP's vehicle.

The RX400h isn't modern - it was launched 21 years ago.

It does not have automatic recirculation. It does not have S-Flow.

The video shows fogging / humidity isn't an issue

The cabin AC/ventilation system has no connection to the hybrid battery cooling system

Servo motor home positions - the system doesn't cycle servos to calibration them, it uses position sensors, plus any calibration would occur on startup, not when driving.

Well said Colin, I was thinking the same and realised straight away it's ai.

1 minute ago, b4u2 said:

Well said Colin, I was thinking the same and realised straight away it's ai.

AI is great has a tool, what it came up with seemed to make sense, some people don't use it, I use it a lot and it does have its faults but what it says here seemed to make, sense. I don't see the problem trying to help someone who maybe doesn't use it, it will be very interesting to see what it is eventually found to be. Systems do run in the background, has this ever been checked as a possible cause?

11 minutes ago, ColinBarber said:

Please stop posting AI slop. It is not relevant to the OP's vehicle.

The RX400h isn't modern - it was launched 21 years ago.

It does not have automatic recirculation. It does not have S-Flow.

The video shows fogging / humidity isn't an issue

The cabin AC/ventilation system has no connection to the hybrid battery cooling system

Servo motor home positions - the system doesn't cycle servos to calibration them, it uses position sensors, plus any calibration would occur on startup, not when driving.

One would hope that any form of help AI or not could help solve the issue, Ok its not 100% correct as I mentioned but can stimulate thought onto what it could be, and sometimes its correct, I personally don't see the issue and nobody else has come up with a solution, it's all about learning and understanding what else goes on in a vehicle, some bits may not be relevant to this but could be food for thought for others, its good to talk and discuss I think!

Little knowledge is a dangerous thing, AI is NOT reliable for fault diagnosis. This is specific to a much older vehicle and as others have said, if a poster is just regurgitating AI nonsense, it's not really much help. Any decent tech should be able to properly diagnose the issue which on the face of it seems to be a section where plastic gear cogs are worn which can be common on older vehicles. Dash removal, if needed, is quite a lengthy and expensive job so the first step has to be diagnostic testing by a properly qualified tech to isolate the part/parts causing the issue before the fault can be priced for rectification.

I never trust AI for car related stuff. Straightforward answers to questions unrelated to vehicles can be handy but that's as far as I go. And even then that's when I have a passing familiarity with the subject. Queries on the US LOC are often answered with a copy/paste from Copilot and are sometimes flat out wrong. Reference to the 4 speed transmission in the LS430 for example.

The RX400h is prime for AI ***** ups because there are non-hybrid models of the same vehicle and AI has trouble differentiating.

4 minutes ago, rich1068 said:

I never trust AI for car related stuff. Straightforward answers to questions unrelated to vehicles can be handy but that's as far as I go. And even then that's when I have a passing familiarity with the subject. Queries on the US LOC are often answered with a copy/paste from Copilot and are sometimes flat out wrong. Reference to the 4 speed transmission in the LS430 for example.

The RX400h is prime for AI ***** ups because there are non-hybrid models of the same vehicle and AI has trouble differentiating.

The key is in making your question include as much as possible, even what country you are talking about. AI is an absolute game changer I use it numerous times daily even for cars, it was AI that led me to the Lexus RX450h+ and then further questions led me to the Takumi model after exhaling in simple and exact details what I would get, a cost analysis and guesstimate of future values. So without it I would never have gone for a Lexus, I always found them boring looking and with boring performance, but AI convinced me the days of racing around are gone for me and now I’m retired a Lexus would suite me perfectly.

I had been looking at the new Land Cruiser but that’s a failure in hybrid model for me, also the ground clearance is poor, it’s tinny, small wing mirrors, aged technology, agricultural engine and had lost the third row replaced by a shoddy battery set up. AI did say the residual values would knock spots off any Lexus in 5 and even 10yrs but even that couldn’t convince me. I also looked at Ineos but poor quality in some places, treated as a commercial vehicle in some circumstances so speed limited on roads, dealer network and parts availability poor, AI also got me to look at the BMW X5, Merc GLE and Porsche Cayenne which I did actually look at, but I have 2 already and decided I wanted something different and ended up with the Lexus to become invisible, as it’s just another jelly mould SUV, it’s not flash but has good heritage which could be at risk soon as all manufacturers chase profits and control of you via their integrated systems, it’s already started on my RX but trust me I saw worse when looking around, soon you will be paying subscriptions for a lot of options already fitted in your vehicle to activate them!

So don’t poo poo AI it’s the future, ignore it at your peril, but use it skilfully, unfortunately I used it without sufficient information so my fault in this case.

I had this issue repaired yesterday at Lextek in Sheffield. Dave is great! He knows his stuff.

I also got them to do a service while my car was anyway in for repairs so all good now.

Ah, good to hear! What was the root cause in the end and how much did it set you back to fix?

11 minutes ago, LexusNelly said:

Ah, good to hear! What was the root cause in the end and how much did it set you back to fix?

It was a faulty Interior Heater Flap Motor Actuator and I bought a used one online and he fitted it for me.

1 hour ago, b4u2 said:

It was a faulty Interior Heater Flap Motor Actuator and I bought a used one online and he fitted it for me.

So was that the number 1 that I posted on my AI suggestion? 😉😀

On 4/26/2026 at 10:22 AM, ColinBarber said:

Please stop posting AI slop. It is not relevant to the OP's vehicle.

The RX400h isn't modern - it was launched 21 years ago.

It does not have automatic recirculation. It does not have S-Flow.

The video shows fogging / humidity isn't an issue

The cabin AC/ventilation system has no connection to the hybrid battery cooling system

Servo motor home positions - the system doesn't cycle servos to calibration them, it uses position sensors, plus any calibration would occur on startup, not when driving.

Oh dear, seen the result of the investigation and result? Apologies will be accepted 😉😀