This has been happening to me (in this case the left monitor). It's been happening about a year now, about 10x / week. The remedy is to unplug the phono plug and plug back in. The problem's then fixed. Now it's happened four times today. Does anyone have any solution to this. Obviously my audio interface is ok on both channels; wiring is all intact, etc. It's clearly an electronics issue in the amp itself. Thanks to anyone who can shed light on this.