Squealing noise around Serpentine belt area

If have a 1998 Dodge Caravan 6 cylinder 3.0 Liter engine with 110,000 miles. I have replaced the serptentine belt about 18 months ago only to hear a loud squealing noise along with a rattling of bearings sound in the belt area when the car has warmed up. The noise disappears when I put a load on the engine but when the car is idiling its very loud. I have sprayed the belt with WD40 but the noise comes back after driving it a short ways. I also have replaced the tension pulley and the idler pulley bearing. Since the auto parts store did have the exact Idler pulley I tranfered the bearing from the new to the old pulley. But this has not corrected the problem. I have noticed this sound on other common Chrysler vans, I am wondering if this a solvable problem. Do I need to clean the belt residue on the idler pulley or do I need to check the bearings on the power steering unit? If cleaning is recommended How or what should I use.
Signed Frustrated!