AC compressor or Idler pulley?
 

2001 CRV 150xxx miles.

The car drives perfectly, AC blows ICE cold air when it's on. Just recently I've noticed that there is a rattling noise under the car whenever I have the AC on. The noise goes away when I turn the AC off. The rattling noise is present at Idle and when I have it between 800-1300 RPM any higher, then the noise goes away.

Any thoughts?

Re: AC compressor or Idler pulley?
 

Could very easily be seveeal things.

Problem with the compressor like the clutch and related parts, could be an exhaust shield rattling, or who knows. Its gonna be pretty hard for anybody to tell without actually hearing it.