Soap (like ivory bar soap) is good for cutting down belt squealing in general. I don't like wd-40 for anything except perhaps bolt and nut removal.

I've seen idler and tensioner pulleys completely shot that didn't really make alot of noise. In any case it's a quick and easy fix. When they go, they make a grinding rattling sound. Like rocks in a tin can trailing behind your car.

I suggest a process of elimination. Remove the belt, and hand turn everything attached to it ('cept the a/c which you'd have to be a gorilla to turn when the clutch is engaged). Try idling with and without the ac on to see if its the a/c clutch.

From what you are describing I would be thinking water pump bearing (look for dried coolant residue), or power steering pump seal, or finally, an alternator main bearing. None of these is that bad. If I had to bet, I'd say water pump.