Monsoon MH500 Standby Mode Problem

I have a set of Monsoon Flat Panel speakers w/sub woofer (MH-500) and it's seems that they are going south on me. What happens is that after some idle time (about 6-8 hours, the noise woke me up at 2am this morning) a loud humming feedback type of noise is illicited. I think that this is happening when the speakers go into standby mode. The mute button and volume control on the puck won't even stop/suppress the sound. I ended up unplugging the speakers and I have been doing so before I go to bed for the last week since it first started. I've had the speakers for 6-9 months and they just started illiciting this behaviour about a week or so ago. Any ideas as to what's causing the humming/feedback noise? The only thing that I can think of is that it's plugged into a power strip (surge suppressor) that's about 10-12 years old. Somehow I doubt that the strip would be causing problems but I'm reaching here...

Any information would be greatly appreciated!

Thanks!