Knocking sound under hard acceleration

[jjpsweet]

Hi.

I have a 2009 is 220d with 110,000 miles. If I accelerate hard in first and second gear, I get a knocking noise from the rear. This does not happen if I accelerate while I am driving at speed only when I am going slow.

Car just had a new dpf fitted by Lexus as well as a service but there was no noise before they got their hands on it. Local mechanic went for a spin and could hear it but was surprised that it didn't happen at speed. Car was up on his ramp and he couldn't find anything loose that could cause it.

Any ideas??

[dougie175]

Is it a single knock or several knocks?

My first thought especially being the rear would be exhaust touching the body (especially with the DPF being done!), often turning corners causes flex and makes an exhaust touch if its a bit too close. However if your mechanic has had the car in the air he would have noticed this I'm sure.

[jjpsweet]

Hi dougie.

Thanks for getting back on this. It's numerous knocks, like someone repeatedly knocking on a door. 

[dougie175]

From what you describe and the fact it only happened since the dpf change for me the first point to look at would definitely be the exhaust touching on the body.

This does create a repeatedly knocking noise as you describe and would make perfect sense.

You need to get the car up on a lift and see if the exhaust is now slightly too close to the body somewhere its amazing how much the exhaust actually moves, especially towards the rear of the vehicle, I have seen exhaust be a good 15mm away from the body and still touch when turning sharp corners and such.

[wahid hussian]

Hi 

Any updates?

I think i have the door knocking sound only mines is250 

Thanks