I'm getting a lot of humming from my living room surround speaker system, most notably my subwoofer.
I have Sharp LCD TV & Onkyo AV Receiver with inputs from DVD player, CD player, Xbox360, HTPC and Cable box DVR. The problem seems to be associated with the DVR/Cable signal and/or the HTPC.
I can best trouble-shoot it with a DVD playing during a 'quiet scene'. I can then eliminate the hum by
1) disconnecting the Sub (faint hum from still present from other speakers)
2) disconnecting HDMI output to TV (obviously unacceptable)
3) disconnecting the cable from the wall
4) unplugging the HTPC (note, i tried putting it on a power strip but even in the off position, it still hums) or unplugging the audio output.
I have a feeling it is an electrical grounding issue... but I don't really know how to approach a fix.
My HTPC was recently upgraded from onboard digital Coax sound to a PCI sound card for surround. Since then, it seems to have gotten worse in that now I also get the hum when watching cable TV & DVDs. I've tried physically separating the cables the best I could, with no improvement. Also I've tried plugging the HTPC in with an outlet from another room, to no avail.
I've had the cable guy out twice, but they seemed to have no idea what could cause such a thing, and were unable to offer a fix.
There are a number of suggestions from various online forums, most seem to point to getting an in-line ground loop isolator; ~$50.
I'm not thrilled about the cost, and I'm worried about potentially degrading the incoming signal? or it not fixing the problem!
I didn't see any discussions on this topic at spcr, and thought it would be good to get some input.