try a buddies spare HU
It is a possibility that you HU has gone south. hook up a home cd player or portable with rca's and listen for the noise. did this one and it worked for me ( teh home unit hookup that is) Also, what about one of the other wires from the HU, other rca's, regular speaker wires , cell phone mute ect touching ground? how about the connection of the rca's to your HU. I have mine taped up to wliminate the possibility of contact with ground. I'd try this forst now that you know the noise is upstream of you amplifiers.
Later,
Chris S.
