Weird noises coming from Subs. Need Help!

I get a wierd beating sound coming from my subwoofers for no reason. My system was working fine one day and all of a sudden I go to turn it on latter that day and the subs just go thump, thump, thump kinda like a heartbeat. It isnt really a hard thump and you can't feel it but it does this even when I have the volume turned all the way down. I turn the volume up and it doesn't get louder either. It just stays on its rythmic bumping pattern. It doesnt even try to hit to the song but ignores the songs bass all together and just sits there and makes that wierd thumping noise.

sounds like your amp is in a feedback loop