subwoofer 60Hz buzz

Hello all,

I'm reaching for your help, please. Upon my return from vacation, I plugged my HT sub (Sunfire Dominator D-8) into the outlet and a relatively loud 60Hz buzz came up. It's not a ground loop, for this buzz is there with the sub disconnected from its input.
When the low level input is connected, the sub still works, meaning that the LF signal is still amplified and outputted, only the buzz is over-imposed and too loud to be ignored. It's not blasting, but not the usual idle 60Hz hum. This buzz is also constant in level, doesn't change with the changing of the level control.
I know it's a shot in the dark, but could I get some advice as to what component might have given up for such a symptom to occur? I have no problem handling a screwdriver and soldering iron, even have a multi-meter, so I could start attempting some component replacement.

Thank you very much.
I had a hum from an 8 ft rca run, tried a shorter cable and rerouted away from ac cables. No problems now.
Thank you all for your posts.
I'm certain there's not an interconnect issue, because the buzz is there even when there's no interconnect at all.
It's also not the outlet, for everything else works OK in it and the subwoofer is buzzy in other outlets as well.
I'm leaning towards the power supply filtration capacitors.
Thanks again.