oil it or shoot a squealer
Either the belt is worn out or the tensioner is defective.
Sounds like a belt or belt tensioner needs to be replaced
Replace with Good Year Gatorback belt. Costs more but worth the money.
Tighten your tensioner pully. there should be a little bolt on one of your pullys.
A squeaky alternator is sometimes a sign that the fan belt or something associated with it is squeaking, not the alternator. (Possibly the belt or belt tensioner) So first I'd make sure it's actually the alternator squeaking before I proceeded. You could try some belt dressing on the belt and see if that helps or changes the squeak. If however it is the alternator, that's usually a sign the bearing's gone out and you will need to replace the alternator.
you dont fix serpentine belts. you replace them. open hood, although it is easier to reach the belt tensioner from under the car, you will need to route the belt from above. Take the tension off the belt tensioner (a breaker bar or rachet and the proper size socket with a pipe to give ya more leverage should work) and pull the belt while the tensioner is pulled away from the belt. to put new belt on, properly follow accesorie pulleys with new belt, leaving the tensioner pulley last once that far, take your breaker bar or rachet with proper size socket... and pull the tensioner away from the belt so that you can slip the belt over the tensioner, push the belt over pulley. release the tensioner and check to make sure the belt is seated properly on all pulleys. Wahlah
Disconnect the battery.Remover the serpentine belt.Unbolt the belt tensioner from the bracket.
Fit a new belt tensioner
Assuming the belt and pulleys are in good shape, put a dab of clear silicone grease on both sides of the belt. Do this with the engine off. Squeak is gone.
GM tensioners are spring loaded to provide the correct tension on the serpentine belt. If the belt is loose, either the tensioner is bad or you're using the wrong belt.
A squeaky belt is usually caused by a bad belt, a missaligned pulley, or something leaking on the belt.
With engine off try putting a small dab of silicone grease on each side of the belt. It works for me.