Well lately I noticed the tone was really bassy but that could be from my new bass. Anyways whenever I turn up the master, even with the bass unpluged and the tuner mute on, at a certain point the thing just begins to HUM LOUD ok I don't want you guys to think its just a little humm I mean as if someone was playing bass with their pickups right next to the cab and overdrving the preamp. It just starts to growl at me which has never happened before. Anyone know whats wrong?