[IVOLIC]

Well mine acted up the other day. Same constant humming noise when the sub is on.
Luckily for me my father-in-law is an electric guru and he told me without opening it that capacitors where the problem.
Needless to say when we did open it one of the capacitors (there are 2 of them,12000 micorfarads) was black at the connection point with the panel.
I am going to buy 2 new capacitors via ebay for $25 and have my father-in-law put them in.
Hopefully all will be booming again in a few weeks!