I have a 2004 Pontiac Bonneville GXP V8. I have noticed that there is a high pitched squealing noise for about the first 30-45 seconds after I start the car and then the car starts leveling. It only does this if the car hasn't been started for a while. I think it has something to do with the leveling, maybe some kind of compressor. Is there anything that can be done to quiet this? It doesn't seem to be affecting anything, I just don't like it. Any suggestions? I did take it to a mechanic who told me they all do that after a while and there was nothing that could be done.

Can you tell where the squealing is coming from?

I can't really tell. It sounds more like a loud whining noise that last for about 45 seconds and then sounds like its winding down and then stops, then I won't hear it again until the next time I start the engine. The mechanic said it was a compressor but I don't think its the A/C, I don't use that.

He was probably referring to the air compressor that levels the suspension. That would explain why you hear the whining when the car is levelling. Other than a new compressor, I don't know how to fix that. Perhaps someone else has an idea? Let'* see who chimes in.

I think what your hearing is the electric smog pump. It runs on cold start up to help lower emissions and it tends to make a high pitch whine.

remove the elc fuse before you start the engine and see if it still does it. probably under the rear seat

I agree...could be either the compressor making the noise or the emissions air pump.....as JW said, remove fuse or disconnect the compressor.....if noise is gone on start up, it'* the compressor...still there, check air pump.....

That'* exactly what it is! I removed the fuse, started the car and I no longer heard the sound. Now I know what I need to do to fix it. Thank you so much for the help!

stick you head under the rear pass side corner of the car while someone turns it on and see if its a leak or just a noisy compressor

I am not sure how the compressor is in your car, but with my PA every year or so I'll get under the car and remove the soft EVAP line going to it, I believe it is the one that goes to the part of the compressor that keeps the air "dry", I'll squirt a few drops worth of this stuff in there.

I know the compressor is designed to be oil-less, but a few drops of light machine oil will not hurt it.
Mine is still running strong, and considering the price to replace the compressor I'll keep oiling it.