[Revorocks]

OK so, after a bit of research, I tried several combernations.

I labled the motor with the problem as bad, and the one I know that works good.

bad rotor + good can = buzz + stiff to turn
bad rotor + bad can = buzz + stiff to turn
good rotor + good can = quiet + easier to turn

So, this leads me to think it must be a problem with the rotor.
Being stiffer to turn is just the magnets in the bad rotor are better I am guessing.

The buzz however would be one of two things, either the rotor is unbalanced, or there is something on the rotor hitting the can, maybe kevlar strands?

I have inspected the rotor and there are some tiny kevlar fibres coming off, but surely they could not cause all that noise...