How do I stop my subwoofer from humming? Watch the above post.

Once you've solved the ground issue, trim the cable(s). They are not well shielded.

Better yet, buy these. I had them terminated with spades and I did not need the black "ground" wire but you can also order a 3 wire version, and only one if you dont need a stereo pair. These are FAR better than stock and cheaper then the REL blue wire or even SignalCable.com

@audiotroy appreciate the suggestion - what I did test is getting all the equipment on the same extension cord. With your suggestion, how would one test for whether there is a ground loop? Am I plugging in anything to the extension cord? 

What is interesting is that the EXACT same configuration works fine w/o for the other parasound amp. 

@willywonka yes I did after Mr. Hunter's latest video, which did not address the issue! Power cable goes off to one side of the REL and the speakon to the other....