It probably was a bad unit, I've had it happen many times with aftermarket alternators. If they make it past the first week, they might be ok for a month or so. To be honest they are junk. I always try to stick with a reman done by the manufacturer of the alternator. I think when an aftermarket company rebuilds them they just clean them up and make them work, not worrying whether they'll last or not.

Just my 2 cents!

Brandon