I just thought of a possible cause for your problem. I have a small powered subwoofer attached to my computer. It has an auto on/off signal sense feature, just like your SVS.

I occasionally notice that it is on even though my computer is off and incapable of generating a signal. I've been able to track this "phantom turn on" issue to two causes.
  1. I have a halogen desk lamp plugged into the same power strip as the subwoofer. When I turn the desk lamp on, it triggers the sub to turn on, as well.
  2. I often leave my cell phone on my computer desk. If my speakers are on when the phone communicates with the cell network, they pick up the signal and I canhear beeping noises through the speakers. The cell signal also triggers the sub to awaken and make noise.
Does either of these causes match up with your situation?