Its a late reply, I know, but I haven't looked at my car for awhile. Its one of the alternator/fan belts. There are 2 that appear to turn the same bearings, so I am unsure how to tighten one and not the other, since only one is loose . Perhaps its a good time to replace all 3 that I have. Surprisingly, I don't seem to have a belt that goes to an AC compressor (not even sure if I have one!). The other belt that I do have goes to the power steering pump.