I just noticed today that the light switch in my garage was buzzing at
100 Hz when the lights (3 x 40 watt fluorescent tubes) were on. It is a
2-way switch ganged to another, that one does not buzz, but the 'duff' switch buzzes in either position if 'on'. I've replaced the switch with another I had kicking around, that also buzzes but to a much lesser extent.
What is going on, for the buzzing to be at 100 Hz there might be a rectifying effect somewhere inside the switch ?