I'm sure the brains amongst LOC will get to the bottom of this....while idling mainly, I can hear a gurgling-type noise which seems to come from beneath the gear shift lever area (though I think this may be a red herring). It's an intermittent noise, present both at idling (most noticeable) but also when in drive. Local Lexus dealer said "there are some particulates in the coolant fluid", proceeded to bleed the system and put in fresh coolant - noise came back after 1 day. I'm taking it back next week but thought somebody might have an idea? Thanks

well i had the same thing happen to a friend of mine with his old aristo.. we discovered at my workshop that the plastic at the filler cap to the rad had fractured and was drawing in air..

A bit of epoxy resin cured the problem for a while but it needed a new rad in the end... best check the top end for cracks etc

possibly an air lock in the system - another loc member recently solved his by raising front of car (ramp) started the car with filler cap off and topped up accordingly.
I had same noise but was due to low coolant level- but as you've just had yours done that shouldn't be the reason.

Thanks guys, makes sense since it was fine for a day after the bleed and fresh coolant.