[steely]

Rob, I think you may have to take it out again and inspect.
Having said that I have a couple of questions: is the ALT back in the car under load from the belt, or does it grind in the housing when on a bench?
If in the car, can you remove the belt and see if it makes a noise?
Move ALT and housing to a bench and test? Did you happen to test spin the ALT before installation?

Or pop the fan and check for scuffing? Sorry no other ideas come to mind.
Good luck.