A few weeks ago, my 2002 Tahoe LT V8 started producing a slight vibration noise from under the hood. Its only a noise - not enough to feel it through the body of the vehicle. The noise is kind of like a hammer drill, but is pretty low in volume (presumably deadened by the engine bay sound insulation), and seems to happen only when the air conditioning/auto climate control is operating and when the vehicle is accelerating. The occurence is infrequent (maybe a couple of times a week), typically happens within the first mile of driving, and the vibration only persists for a few seconds. Obviously, this makes it difficult to diagnose.

As well as the noise, I have noticed that the A/C always seems to be blowing cold air, even in manual mode with the A/C LED "off". I live in AZ, and so with outside temperatures in the 90s, I know when the A/C is blowing cold .

Can anyone shed any light on this phenomenon ?

 

This is usually caused by a vibration coming thru the exhaust system depending on engine load and normally happens during light acceleration up to around 2,000rpm's with the A/C on.

If so you may want to have the dealer reference GM document TSB # PIP3121E.
If your Tahoe is out of warranty ask the dealer for a "good will" repair, in which GM will either cover the cost or split a portion of it with you depending on the miles.

The HVAC system is designed to run the A/C compressor if the Recirc button is activated, when you feel cool air is this case?