Line level isolation transformers can be found economically at most car audio shops; they have RCA in's & out's. These will isolate the audio shield connections from the hyper-ground noise which you're experiencing.
Sometimes though, all you have to do to fix this is to ground the coax's shield to your household ground. Use a length of stranded #20 awg wire, strip off some insulation & attach one end to a household outlet's cover-mounting screw, then strip & wrap the other end around the coax connector's shield, securing it with a small cable tie. This brings the coax';s ground potential equal to your household ground, which completely solved the problem for me. I still use the audio coupling transformers as extra insurance, though it may not actually be necessary.
