Hey guys, got a serious problem here. I have a Randall RX120RH, haven't played in about a week. I turn my amp on, and it starts producing a weird noise. Its a pulsating sound, really audible, almost sounds like a helicopter. I unplugged the instrument cable, and it still makes the sound. I unplug the speaker cable and the sound stops, even plugging into a different cab results in the same sound. Obviously its an issue with the head, but any idea of what it could possibly be?