Subwoofer HUMMMMM

even when nothing is connected but the power cord
The plate amp probably went bad. I had that happen to me.

I have seen ads on e-bay for repairs if yours is out of warranty.
@stringreen. I don't see any subs. listed in your virtual system.  A fine system indeed!!   What subs. do you have?
I have a 5.1 system in another room......Denon/Sony TV, with NHT speakers, there are 2 speakers in the ceiling of every room in the house for background music
jperry...thanks - that’s what I suspected. Although the sub was (not now) in the system, I don't hear any sub contribution.... The manufacturer will repair it for 150 dollars or so.....I just have to send the back of the sub to them. I’m thinking of having someone local take a look.....
It could be as simple as a bad cable or connection.  How loud is the hum?  Does the sub still function?
big_greg......not thundering, but very annoying.  
Sorry, I missed the part about even when "nothing is connected".  I've had my subs hum because of a bad cable or poor connection, but if you don't have a cable connected...
Have you tried a different power cord?