I had the same problem with my new Axioms and Denon receiver. I found the problem was caused by a (A.C.) ground loop. The HSU VTF-2 amplifier uses a 3-prong grounded cord, the receiver only a 2-prong,ungrounded cord. With the LFE cable connected to the subwoofer, you're effectively grounding the receiver through the sub. Try using a 3 to 2 prong "cheater". It eliminated the problem for me. Good luck!