Bosch Axxis Condensing Dryer motor shaft shifted???

[JazOfAllTrades]

Hi there, here's a stumper: My Bosch dryer drum stopped turning, with a burning smell and smoke.  Figured the motor seized and blew, so I took it apart to see if I could remove/replace it.  I discovered that what had happened was the front blower wheel (the smaller one farther inside the machine than the one on the back) had begun spinning against the housing, grinding itself down and causing the burning and smoke, eventually preventing the motor from turning at all.
I can't figure out how this happened or how to fix it.  Nothing is out of place, the motor didn't shift on it's mounts, and neither of the blower wheels seem adjustable forward or back.  The only other evidence is that the smaller drive belt looks like it was rubbing against the motor, so it seems like the shaft has moved somehow, but it doesn't have any play in it either.  Has anyone encountered this before?  Advice?