hum coming from my subwoofer

You have a ground loop caused by your satellite reciever.
As Warrenh suggests you can ues a three to two cheater plug on your sub which will lift the ground or buy a ground loop eliminator. A ground loop exists when two or more grounds have a slight difference of resistance between them. This produces a voltage drop which will produce hums in your sub and possibly other gear. Hope this helps and Happy Holidays.

A friend of mine had a similar problem recently. He traced it to a loose ground connection at the cable tv input on the outside of the house.

Does your sub still buzz when turned on - on its own, with nothing hooked up to it? Unplug everything from the wall- including the cable from your amp or receiver(turn it right up). if it still hums or buzzes than it is an internal problem in your sub. It should be absolutely quite on its own. If it is buzzing while hooked up to other equipment - you probably have a ground-loop problem. any of the suggestions above may help. Or just by making sure that there is only one grounded piece of equipment plugged in.