In my previous post on Ground Loops and Power Line Interference Hum, I mentioned another common complaint in Home Theater setups:  "Hiss" from your speakers.  Hiss comes from Radio Frequency Interference (RFI) -- i.e., higher frequency signals emitted by something in or near your Home Theater setup.  If these emissions get past the shielding of your electronics they can result in audible Hiss from your speakers, even when you are not playing anything!

If you'd like  more info on what's going on, and suggestions for how to deal with it, this post is for you!