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'm not an electrical expert but could it be the electrical outlet itself? Maybe it's cracked ever so slightly inside or maybe it saw a power surge while you were away on vacation and became slightly damaged. After all, most are low cost contractor grade outlets. Have you ever considered upgrading your electrical wall outlets to for example a PS Audio Power Port? I've upgraded all of mine to these Power Ports where I have my audio and HT systems plugged in. Sound is all crisp and crystal clear. These ports use hospital grade internals and sell for around $50.00 each. Another question: does your sub-woofer interconnect cable have a separate ground wire where you can connect the horseshoe clamp to a screw on the rear of your amp or receiver? I believe you could still get some buzzing even if the input is disconnected. Not 100% sure but could be. I have to subs and both use interconnects with a third ground wire (AQ brand)
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.