make sure the two pulleys are actually parallel to each other as well as inline with each other. i use a small keychain laser beam that i got at the hardware store, it is about 1/2" dia. and about 3" long. i lay it in the groove of one pulley and it should point to the center of the groove on the other pulley, and it self-centers itself. if one pulley is cocked slightly it really shows up. you have to do this with the belt off and then make sure the pulley doesn't cock itself when you put the belt back on. squeals can show up when the belt has more traction on one side of the pulley than the other. if they are lined up, belt is good and have the correct tension they should not squeal even on a slick pulley.
about my laser, i have tested it by rotating it in a pulley and pointed to a stationary marked spot, so i know the laser is comming out of it's holder in the center of it.
