Here's a story for ya:
I might be quite wrong about where the noise comes from... face/palm.
When not in use, I slide my wheel on a shelf of a small bookcase next to my chair. When I plugged it in the other day, it autorotated itself off of the shelf. I had my back to it, I did not see how it hit the ground, the only thing I knew, my new wheel, was now making one hell off a racket when rotating.
What The Efff Just Happened!
So I took it apart... the whole thing into pieces. With each motor in my hand, I applied voltage to them, one was running silently... perfect, the other was turning but the torque was on/off/on/off/on/off/, it had a rotational shake to it and was quite noisy. It was finished, I needed a new motor. I opened it up, hammering at the lock tabs, being careful of not bending the brushes while pulling off the back end... full inspection... nothing. I looked at avery bit back and forth... nothing. I put it back together, hammering the tabs back in, power... trut-trut-trut-trut-trut... done for... passé. In a fit of frustration, while the thing was shaking in my hand, I took the hammer and whacked it on the side.... bzzzzzzzzzzz... all nice and running smooth like the other one. Well that was 6 hours well spent! Next time something does awry, I'm just gonna take my hammer to it.
So, I put the whole thing back together and it's there that I noticed a gap. where the main bearing of the wheel shaft comes through the back metal plate of the motor/gear box. The bearing and back plate at 9:45 in the first clip. That hole is more than a few thousandth bigger than the bearing itself. I now think the noise comes from the bearing moving around in there. When I saw that, I "Tried" to made a shim out of the side of a beer can, it was all tight for a few weeks but it didn't hold, beer can aluminum is way too soft.
I'll see at the next tear down..
HF
I saved / fixed my wheel... Mouhahahaha... I am so good!