Hi blondespot11,
First, good detective work on your part in isolating the source of the hum. You have a classic case of "ground-loop" hum,which is caused by a voltage differential between your incoming cable-box signal and the ground for the electrical system in your home.
You can get rid of it easily with one of these Axiom ground isolating transformers:
http://www.axiomaudio.com/groundisolator.html Before you order it, you can try plugging your subwoofer and or your/AV receiver into a different electrical circuit than the one for your cable box--try a different AC plug across the room, if possible. That may do the trick. If the hum is still present, you'll need the isolating transformer, which, by the way, will pass all Hi-Definition digital cable signals (and analog video too) with no degradation. It has a bandwidth up to 1.5 Giga-Hertz. If you're interested, here's a detailed article I wrote on ground loop hum troubles and how to remove them:
http://www.axiomaudio.com/tips_eliminate_hum.html Regards,
