Magnetostriction. It’s usually another item in the home that will cause amp hum (not heard through the speakers)
Most common items are:
LED lights, Fan Speed controls, Some lamp dimmers, proportional temp controls on old range tops, coil heaters with thermostat fans, etc. None should be leaking DC back into the mains but they often do.
Most common items are:
LED lights, Fan Speed controls, Some lamp dimmers, proportional temp controls on old range tops, coil heaters with thermostat fans, etc. None should be leaking DC back into the mains but they often do.