A/C compressor squealing

My truck is a 2wd 2001 with the 2.4 engine. When I start the truck, and occasionally when the engine is at higher RPMs while driving, a loud squealing noise comes from the A/C compressor or, I'm hoping, the clutch. It's particularly bad when the engine is cold but it never quite goes away. I always get the squeal whether or not the A/C is running.

I replaced all the belts and they're plenty tight, for a while they were probably a bit too tight as I thought they were the problem and tightening them did help temporarily. I tried dripping water on the belts as the engine was running, to no effect. I removed the belt going to the compressor; no squealing.

There is a slight wobble in the compressor pulley that mostly went away when I hit it with some WD-40, but the squealing is still there. I checked before doing this and haven't seen any oil dripping, and the air is blowing as cold as ever. This problem has been slowly developing since last summer, so I would imagine if I were leaking refrigerant it would be long gone.

Has anybody had this problem? Is there anything else I should check? Any idea what exactly the issue might be? It's not the end of the world if the compressor needs replacing and all that entails, but I'd hate to go to all that trouble and expense if it's just the clutch or something else I haven't considered.