why is this thing humming?

Try this thread also. Sounds like a ground loop hum, and the hands-down most common culprit is a coaxial cable (TV) feed comming into the same circuit. Had the same problem, and the linked discussion (as well as many other's you'll find) tell you how to lick it -- if that's what's ailing you.

I turned on a movie this morning and the hum is very apparent in the sub woofer also. Probably louder for the most part through the sub. Now im getting aggervated.ahhhh.Thats better does this change any thing? I tried changing the sub cable and it did nothing. I had a sub cable befor that waqs the cause of a hum on a previous system but this time no luck. Thanks in advance Matt

try ground isolation transformer in line on your CATV.

AAAArrrggghhh! Jond beat me to it!

Check and see if you have a light with a dimmmer/rheostat on it, plugged in somewhere in the house. If so, unplug it and check your system again.
Let us know if you find the cause?