I don't suppose you might have forgotten to peel the warning sticker off it? I've seen people do that so many times its not even funny anymore.

If it needed reaming to fit the shaft, is there any chance you reamed the hole out a tad too much and its mounted off center as a result? This is another common theme I see all the time.

FWIW, I've seen very few MA's that were actually balanced to my satisfaction right out of the mold.