Can anyone help with noise which is produced by my denon sub. I have the 487DV -Time Warner cable into a HD cable box, then into Denon receiver with optic audio cable into a Panasonic plasma. When playing tv I get random thumping, druming type noise on various programs in dolby digital setting. At times it almost sounds like backround music rather than random thumps. I have adjusted the volume and tried different settings with small, large speakers. I purchased a heavy sub cable but noise is still unbearable. I tried changing power outlets. Denon advised it may be a crossover issue in the sub and the whole system would have to be returned. Any other suggestions before I return the whole setup and grow back hair I pulled out? Thanks chas