I don't know about an official name, but one cool tidbit is that the frequency is tied in to the frequency of the electricity powering the device. I was thinking about this yesterday because I noticed that the noises from the air-conditioner and from my vacuum resonate to an irritating squeal.
I be curious: why do you want to know?
ADDITION: A quick google search suggests that the name is "electric hum," or simply "hum," since techniques to reduce the noise go by names like "hum-cancellation" or "humbucking."
