First try using some Ajax cleaner,powder form. This work's to stop the squelling. Any other noise could be bearings.
Some take the belt off and deglaze the smooth side along with the smooth sides of pulleys.
97 GC 3.0
2boys.dozen'z of friends hauler
If it's chirping then its because a pulley is out of alignment with the others. Usually this is because the tensioner is going bad. It starts to bend and throws off the alignment. Also, with some Ford trucks they've had better luck with replacing the belt with the OEM belt or a Goodyear Gatorback. They claim the Gates belts have problems with squealing.
I use tri-flow oil on mine but I don't suggest it for anyone else as it can throw the belt off of the tensioner if it's bent.
My serpentine belt noise was driving me crazy. I tried spraying WD40 and Windex that made it go away for a few seconds but nothing like Comet! After doing a search that hinted on Ajax, I tried sprinkling Comet on a plastic teaspoon and on to the idler pulley with the engine running and the chirping disappeared like magic. I even took it on a 15min test drive and still no noise.
I had a squeal on my 5.2 dakota driving me crazy. Changed my tensioner and pulley, idler pulley, new belt and still squealing. Threw a little baking soda on it.....poof....squeal GONE . I'll let you know how long it lasts.