So I replaced y altenator. Belt is good and all. But now it has a whining noise that I'd quite noticable. I know its the alt cuz it gets louder when decelerating to an idle or when accelerating quickly... Any suggestions?

 

Get it rebuilt...or if there is a warranty, take it back.

 

return it, and if it came from autozone, get your money back and go buy one somewhere else.