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if the noise goes away with the water test, the serpentine belt can be changed easily (on the 2.0 at least). If it fails the water test, then it's most likely the bearings wearing out.

The compressor is a possibility. If it's more than 100K miles and you use the A/C consistently, you'll need to replace the entire compressor. Shouldn't be too difficult except you need to vacuum the entire system (in a environmentally friendly way), and you're supposed to change the dryer once you expose the system to the open air. Otherwise, the moisture in the atmosphere will get in there, and since water doesn't compress, it'll break your new compressor soon after. And of course, you'll need to refill in the specific amount (by weight) of refrigerant afterwards.

You should also check other things along the belt path like the alternator, the tensioner, and the power steering if you don't have electric power steering. Take off the belt and spin them. If they aren't perfectly smooth or you hear some metalic rubbing sounds, then you've found the source of the noise.
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