I have a Sunfire subwoofer that's about 4-5 years old. Recently it has started humming (60 cycle). The hum occurs right after it produces any significant output. The hum remains for about a minute, then goes away on it's own. If the sub is plugged into the same circuit as an incandescent light, turning the light on will immediately silence the hum.
Can anyone tell me why this might be happening? If it was a constant hum I would understand, but this thing with the light is really puzzling.
I have tried plugging it into different circuits and lifting the ground, but to no avail.