Gfs 2006 Chevy Malibu had an old serpentine belt so I changed it out and it worked great for a day or so then started squealing again. It used to do it only under load with the AC on and such now it squeals for a second when started then finally will go away.
One of the pulleys the belt goes around is out of whack guarantee it 100%
Check them all, the water pump, the alternator, the crank pulley, and especially the tensioner that’s the one that normally goes bad
That’s why the new belt is wearing weird because one of them has some sort of play in it