Unless the vee portion of your current belt is sitting on the bottom of the vee on a pulley. You have over tightened the belt and still have a noise. Sounds like it is other than a belt issue.

If you take a bar of face soap and rub it on the vee portion of the belt with the engine off. If there is still a belt problem with the belt having decent tension. You problem is elsewhere usually.

It still sounds like the alternator is working far too hard. Yet the output is not showing up at the battery. Exciter voltage somehow is too high? A disconnect of the wire might make a difference. You have not boosted with a jump start in reverse polarity and shorted the diodes inside the alternator?