based again on the limited run I did, I can't see a reason for the low speed other than noise.

It faked me out into thinking it was the regular speed, till I heard regular speed later that day.

If it ran for 2 days, and you didn't notice any issues, I would still try and return it.

If you smoke the replacement, then try feet's idea.

I guess the other question is, how long was the actual total run time. That is you had it hooked up 2 days, but did it run 1 hour or 8?