Now when you say it just developed a hum, did you add anything new? Are you using cable tv? That is usually the culprit for the hum. Although the sub is the component producing the hum, it is most likely not the cause of the hum. This is more likely than not a ground loop issue, for which you will need to try a ground loop isolator or cheater plug thingy. I don't have any links handy, but if you do a search, you may find more info, since i think this issue comes up every so often.