Help! loud screeching sound that stops when I disconnect the battery

Hi, the alternator in my Nissan Sentra recently died, I was able to replace it but now there is a loud screeching sound every time I turn my car on. I found that the sound stops when I disconnect the battery and leave the car running, however, when I reconnect the battery the sound comes back on. I also found that if I just leave the car running, the noise eventually stops on its own and the car appears to run perfectly.

Any suggestions on what might be going on and how to fix the problem would be greatly appreciated.

Thanks.

um, slipping belt - needs to be tightened?

but then what would cause it to stop when he disconneccts the battery? that is wiered ive never heard anything like that before

Hows your starter??? I understand that it still works, and starts the car.... but years ago, on my first car, a 92 cavalier, the starter went on it, and there was this loud grinding, buzzing sound, that went away as soon as the battery was disco'd...... maybe your starter is about to give up the ghost as well.

but then what would cause it to stop when he disconneccts the battery? that is wiered ive never heard anything like that before

because the load on the alternator drops, so the load on the belt drops too...