Aweful Niose, Need Help

I just got done replacing the alt. on my friends 1990 SC auto. When we went to go start it, it fired right up, but instantly starting to make an aweful screeching sound. It kinda made the same sound as when you hit the starter when the car is already running. Anyone have any ideas what to look for. The car ran fine, just made this terrible niose.

Thomas

Pull the belt, start it and see if the noise goes away. Just run it long enough to see if the noise is gone. Might have gotten a bad alternator.

Also could be the belt is slipping. Either the belt has stretched or is glazed, or the tensioner is bad.

Thanks guys, I'll try those things before dropping the starter. The alt. was rebuilt, and not a new one. I guess it's possible something got put back together wrong. I'll give that a try and see what I find out.

Thomas