Thanks for the help here. I've greased both bearings and am still getting the whirring noise. It's pretty hard to tell exactly where in the motor the noise is coming from. Possibly the brushes rubbing against the commutator? Can they be shaped/ replaced/ adjusted? Any other ideas would be...
As this is a handheld mixer, there is no belt drive. The paddles are turned by two gears that are turned by a worm drive on the motor shaft. As for the "other bearing," I did locate a race (with no bearings inside) at the other end of the shaft (thanks!), but it also shows no signs of wear...
I took apart the motor assembly as far as seemed feasible and (forgive my ignorance at what I'm looking at) found only one bearing and it didn't seem worn. It was located at one end of a shaft where the shaft fits into a socket. I'll try to describe the parts of the motor to see if it gives...
My electric kitchen-aid mixer recently began to make a high pitched whirring sound that increases in pitch with the speed of the motor. After disassembly and cleaning, all of the parts seem to be damage free and operational. Any ideas what could be causing the noise?