This problem just started. I have my satellite audio running on a 5.1 surround setup through my Sony receiver. I am getting a terrible hum through my two rear channel speakers only. When I switch off the TV it goes away completely. If I turn my surround off the other speakers work fine.

What could this be? I've checked all the connections and am thoroughly stumped.

Thanks

They may be near some type of interference, or the speaker cable may cross some interference i.e. electrical wires? Not sure if you can blame it on the tv. Have you run the surround in the past with a different source and it performed correctly?

Sorry for the double post on this...the server was having issues earlier. If a mod could please delete my other post that would be great.

The surround has always worked fine in the past even with my CRT display. It was working great with the plasma too then it just happened all of a sudden. None of the other speakers are affected, only the two rear 5.1 channels.

I would have first suspected a ground loop,
but let me be sure I'm clear:

TV on, surround, hum
TV on, stereo, no hum?

That would be weird. If it just hums whenever the TV is on and there is any path between TV and receiver, I would check for and eliminate any potential ground loop.

Note I had and solved a similar problem: terrible hum if plasma and pc were both on.

Mike

What are your connections (analog, digital) to the TV and the Sony?

Here's how it's setup:

- STB S-video to plasma input 1
- STB composite audio to Sony receiver
- Sony DVD player composite audio to receiver
- Sony DVD composite video to plasma input 2

So there are no audio signals processing through the plasma. I'm thinking maybe I need to run the audio into the plasma and back out to the receiver. Again, the only hum I get when in surround mode is through the two rear channel speakers. Switching off the tv or disabling the surround eliminates the hum/noise.

I'd be interested in hearing more about the ground loop. I'm going to try disconnecting the s-video connection and see what happens.

Ok, I just pulled the s-video and the hum goes away. I think I may need to run the STB audio through the TV to do this correctly.

Correction to the last statement. When I disconnect the s-video cable the hum gets quieter, but only goes away completely if I turn off the plasma.

I just thoroughly went through everything trying different connections and no matter what I do if the plasma is on and I have the audio running in surround the two rears hum bad. At this point I almost feel my receiver has gone bad. Something to do with shielding for those two outputs or something. I'm just blown away that when I switch the power off on the plasma the audio clears up.

The only thing I didn't try because it doesn't look right to me is running the audio from my STB to the plasma then out to the receiver.

I wouldn't think something went bad in the plasma. It's got a low hum that I consider normal, only really noticeable if you poke your head near the back, but it matches the hum of the speakers. I am leaning towards some type of component failure though since this trouble happened suddenly. Lets hope it's my old Sony receiver. Didn't want to spend any money on upgrading this just yet though.

I found some good info from the Hum faq thread in the audio section. I will be pursuing a possible ground loop issue.

Well I seem to have fixed this issue.

I ended up running my audio inputs to the tv and then from the tv to the receiver. The buzz went away. I'm still not sure why it happened in the first place since it wasn't happening for a week or more when I had it hooked the other way.

It's hard to tell. These things can be counterintuitive. To figure it out would require a list of every single connection and which components have three prong plugs.
BTW I solved my problem by switching from coaxial to optical audio connections to the pc - completely removed it from everything else, electrically speaking.
Mike

I have been having a similar problem. The hum has been coming through my subwoofer when ever my Panasonic plasma is on and there is surround sound selected on my receiver. No hum at all when the Plasma is off. I think I have eliminated the hum! I went and purchased a cheap snap on RF Choke from Radio Shack and wrapped it around the power cord to the sub. Now the sub is virtually silent when there is no bass output. I will know tonight after everyone is in bed and there is silence in the room if the hum is 100% gone.

Thanks for the feedback brigsby!

I still have some minor hum coming from my rear speaker channels in surround. I noticed it more when I played a DVD the other day. I may end up eventually trying one of the RF isolators from Radio Shack.

All of these sound like ground-loop hums, which can be tricky to solve. Often the problem is the cable company ground not being tied directly to the main house ground, but it can be also caused by different devices having different ground schemes (some use 3 prong plugs and others use 2). From my experience, hum can also be generated by a device itself, such as transformers in amplifiers (subwoofers are especially susceptible). This link may help:

http://www.audioholics.com/techtips/setup/avhardware/groundloopcableTV.php

Thanks for the link dsmith!

I have checked my cable ground and it is indeed only grounded to a water line. It's very close to my power meter, but there is no exposed grounding rod to run a quick connection. I'm almost wondering if my home AC is grounded to the water line. A check inside my breaker box reveals the grounding bus, but no idea what it grounds to from there.