Update --if anybody cares.  I didn't get any responses and calling Bachmann just pointed me to resetting the decoder (setting CV8 = , which I did; no joy.  I had an old Digitrax DZ 126 laying around from an earlier to-sound conversion, so I removed the Bachmann factory DCC board and soldered in the DZ 126 --works fine; no vibration/hum, no sounding like a bad toy!! 

I have acquired a Bachmann GE 70 Ton DCC switcher.  It runs poorly.  I've disassembled it to the point where the motor is only turning its flywheel --both fore and aft drive shafts disconnected.  Using my NCE controller, as I increase speed, the motor just hums/vibrates loudly for the first two-three speed notches and then begins to turn around the fourth speed notch --and continues loudly.  Is this a DCC decoder issue or a motor issue?  It is really unusable in its present state --runs like a cheap, bad toy and not a representative model.