Belt pulley squeal

SOURCE: timing belt/water pump

it sounds like who-ever put it back together again never tensioned your alternator belt properly and thus when its cold you hear squealing. The hum could be the belt rubbing off of the timing belt cover if that was also put on incorrectly i would think.
It would be beneficial to have it all rechecked before driving it again just to be on the safe side.

SOURCE: i have a 91 626 mazda, timeing belt broke and the

Check the ECM for codes. Cam or crank sensors will cause a no start. Also there should have been a compression and/or leak down test performed on the engine before the belt was replaced. This is done to make sure that the pistons didn't bend the valves. Bent valves will cause a nostart because of no compression. First check for codes then do a compression test before you replace anything. Let me know
Randy

SOURCE: I have a high pitch squeal from 1998 buick 3.8,

i have the same problem, changed the alternator, pulley and all that, it happened after i had the intake changed out due to the egr problem, if yours hasn't been changed id look into it before it goes, better sooner than later sorta things...

SOURCE: belts sqealing

If you are talking about the harmonic dampener (the big one at the bottom) it IS supposed to be one piece. If the outer part has torn away from the inner then you had better get another one before it flys off and tears something up. NO pulley should just fall off when the belt is taken off.

SOURCE: mazda protege 2000 squealing from serpentine belt area check engine light on

it is the belt it is either to tight or not tight enough