squel from belt area when idling?

I keep having this squelling from seraptine belt when I am idling then when I accelerate it is not as loud. I did replace the belt and the belt tensioner assembly that did not make any differance. I used belt dressing that seems to quite it down to chirps rather than a loud squelling. I did have the alternator checked out and passed the test that autozone does.

Any ideas of what it could be and any remedy to fix the problem?