I have a 99 blazer and sounds like the belt squealing replaced belt, tensioner, tensioner pulley, idler pulley, alternator. Replaced water pump and noise went away but after running for 15 min it came back. Please help!
Get a spray bottle with some water in it and when you hear the noise, spray a little on the belt and see if the noise disappears. If it does, then you still have a belt problem. If not, look elsewhere.