Thinkgood,
The industry usually calls it "60 cycle hum" because it is caused by 60hz power. The reality is that it is really 120hz (or 100hz for our friends across the pond) hum in transformers and coils, and flicker in fluorescent lighting.
The 120HZ hum is a result of the magnetizing current of the coil going to zero every time the voltage goes to zero. The voltage in a symetrical waveform crosses the zero axis 2 times every cycle.
