I had the famous squealing belts. When I put on the AC or used lights and wipers, I would get the belt squeal and then it would go away. Changed the belts, alternator, battery, and even the crankshaft pulley. It always came back.
The water pump gave it up finally on my car (lots of antifreeze coming out) and when I went to change the water pump and the Timing belt, I noticed oil had been dripping from the cam seals down to the pulleys. It was not enough to notice by itself without actually looking for it. While I was there, I replaced the cam seals ($10.00 in parts and less than an hour. EASY.). I inspected the pulleys and belts and they were coated with oil. Cleaned everything with degreaser. Not one squeal in three months. No matter what I do, no squeal. Check the bottom your engine below the cams for oil if you have a squeal. Leaking water pump can also cause the problem but that should be obvious due to large amounts of coolant loss.