I use s-video, but I can try to disconnect it and let you know.
--- I just checked, no affect.
The only thing I notice, is when I unplug the unbalanced line from the sub or the SMS, the hum stops. I even tried to lift the ground on the sub and then on the SMS, no affect. I unplugged all the obvious Coax (Sat & ant) from the system, still no affect.
The mic/combiner spliter gizmo arrives on Thrusday, I hope it does the trick.