Took the belt off to check the tensioner, the tensioner seemed fine, but the belt was shot, so I bought another one. The drive belt was shot too so I bought one of those. Let me tell you, it is the biggest pain in the butt to change the drive belt, the darned tensioner takes a really large star bit, and the tensioner is right in the middle of the assembly. Took me about an hour, and lots of cursing to get that belt back on. Well guess what, with the new belts, the noise is gone! I think what was going on, is the belt was so cracked that the surface was no longer smooth and was vibrating the tensioner. Whatever it was, it's fixed now! Funny how if I would have taken it to a dealer, they would have told me the compressor was shot and needed replaced ASAP, and you know they would have put a new belt on too, so $1,000 later they could say they fixed it when all it needed was a new belt!