I cleaned the motor and very small amount of carbon off the commutator, and cleaned the shafts. I made sure the bushings had oil, but not too much. The bushings were not worn. The motor turned easily by hand. After reinstalling the motor the noise was no better. I looked up a local sewing machine repairman. He told me some of the cheap USA made motors could do that and suggested that I change the motor. So, I bought a $20 low mileage Kenmore motor and installed it. No more noise.