i recently replaced the 2 idler pulleys and the tensioner pulley.
in the wk following, with the aircon ON, i have developed a rumbling sound when idling in gear........Idling in park there is no rumble
Idle speed drops 50- 100 when put in gear and rumble goes away when revs increased
when in gear turning the aircon OFF reduces the noise. (remember no noise in park with Aircon ON)

as no noise with aircon ON in park i am thinking the Aircon compressor is not the fault

I am thinking the actual tensioner being "loaded up" is the cause. 2nd thought is engine mounts.

Any other thoughts are most welcome

 

i just found a post on another forum (not lexus ) that had the same problem ( noise only happens when in drive ok in park) this is the video he posted identical sound to mine


he states it was bearings in the alternator My car has 230k kms so could ?

any thoughts?

 

A good posibility......A stethoscope or a long screw drive on the alternator w/ the engine idling, as that'll amplify the growly noise.