check your wheel bearing
The differintial is starting to wear...
My trombone does not make a humming noise. Does yours?
Most ceiling fans make a humming noise. If you feel the humming noise is unusual, you should check how attached the fan is to the ceiling, as the vibration of the fan can cause a humming noise.
Probably seized up or single phasing.
Most likely the humming noise is coming from a contactor located in the outdoor unit if you hear the noise outside or from the air handler or furnance located inside the home,if the hum is inside the home
they make a humming noise
the humming noise is coming from a bad ground on you stereo
its probably your radiator
Purrrrrr and humming noise