I just purchased an 03 H2 with 55k miles. Everytime I start it, there is a very loud and disturbing noise coming from under the hood. It sounds like a loud air compressor and only happens after the vehicle has been off. The longer it is has been off, the longer the noise occurs for. Usually about 15-30 seconds if it's been off for hours, if it's only been off for 30 mins, maybe 5 seconds of the noise.

I measured the gap between the top of the rear tire and the wheel well and it's 8.5" no matter what, so it doesn't seem as if the back end is going up or down at all.

Anyone know what might be the issue? I have a 3 month, 3k mile warranty from the dealer so I plan on having it looked at by them but I'd like a heads up as to possible causes?

 

The air compressor is located behind the rear bumper, So I doubt its that causing the noise, my rear tire/ fender measures 7 1/4 but I have 35" tires, so that would be about right,

 

You're right about the compressor. I did some testing and that works fine. Ride height and rear accessory inflator both work fine. So something else is making this noise. Any ideas?