Feedback from surround sound

Hey guys,

When I have my iMac (new model - thin design) hooked up to my surround sound while it's playing music there is absolutely no interference and it sounds great but if I pause the music and the computer makes no sound, after about 30 seconds a dull buzzing sound will happen through my surround. It does not happen with any of my video game consoles or while watching TV. I'm not sure what would cause this, I know that sometimes if you run the audio cable beside a power cable you can recieve interference that way, but it's isolated from all power cables. If anyone has a similiar issue that's found a resolution please respond.

Thank you