I'm having a similar issue, when I have the coax going into my cable box get loud buzz from my current B&K which uses rcas, but I get nothing from my Odyssey which uses balanced. So I do believe in the ability of balanced to reject noise, and this in a short run of only 3 feet. Long live balanced! I will probably get the Jensen isolator anyway, just to be sure.
_________________________
Current: Denon 3311ci, Anthem PVA 5A amp, Ascend Acoustics Sierra stereo mains, Ascend Acoustics 340 center, Aperion Surrounds, LG Plasma