Re: I found out the source of the squealing noise from the belt side
I just bought an 02 Taurus with 127k miles from the Dept of Transportation and it had LOTS of dust in the interior from gravel roads. After 1 week the belt started squeaking. I used the old school method of putting a hose to my ear and pointing it toward the loudest squeak. I narrowed the squeak down to the belt coming out of the water pump. I took the belt off and noticed tiny bits of shiny gravel stuck in the ribs of the belt. I picked them out (probably 100 of them), reinstalled the belt, and the squeak disappeared! Much thanks to the other post in this thread for suggesting this!
I'm an ex-belt engineer from Goodyear, so I was actually surprised it was the belt. We all know belts are made of rubber and that all rubber squeaks. So the auto companies take great pains to avoid belt squeak. Most new belts don't squeak because when the ribs are ground/milled at the factory this milling process exposes the tiny fibers (cotton, polyester, rayon, kevlar, etc) in the belt. These fibers help contact the pulley grooves. They allow the belt to slip a little and not squeak. Problem is that after about 10000 miles the fibers tend to wear off and leave exposed rubber - which squeaks.
Since I had such an old belt and it just started squeaking, I was surprised it was the belt. I thought for sure it was going to be the WP pullley. So if you owe a Taurus and drive gravel roads, don't be surprised if the belt squeaks at the WP after a while . But clean out the gravel from the belt grooves, and you are good to go!