Seems to happen when I'm coming to a halt or accelerating from a stop the most. It seems to be coming from the front passenger side of the car. It can also happen when I am waiting at a light fully stopped. Any ideas what it might be?

 

I've noticed it too - almost like a compressor is kicking in somewhere (even with the AC off). Could this be something related to cooling the turbo?

 

I just noticed it recently though. I have 3,000 miles on my RDX. How long have you had yours and did you notice it from day 1???
Thanks

 

I have 500 miles on my and when I have it idle with no AC on the car is real noisy. Some kinda compressor coming on and off. Anyone know what it is happening?

 

I just thought that was a fan of some sort cooling something off. But it can kick on and off every few minutes. It does it a lot less than when I first picked up the car a few months ago.

I'm not sure I would call that noisy or a vibtration sound though...

 

I've always thought it was the AC.

 

http://www.in.honda.com/Rjanisis/pubs/SN/B061000.PDF

See page 1....it should help answer your questions.