Take a look at my video to get an idea of how to open the Sunfire MK2 properly and also get an idea what sort of dangers live inside the box. There are several fixes that have worked for me in the past and one that is not working now.
Hi, I had the same problem as this, the fix was quite simple and the hum never came back.
If you pull straight out on the sub amp's volume knob it will slide off, then to fix the hum, tighten the nut that is behind the knob on the potentiometer and your hum should go away. My hum went away and never came back after this fix. Hope this helps you.
Easy. Your home theatre amp will have a sub or LFE output ( RCA plug ). You simply connect this output to the input ( usually the left side, or use a Y splitter and use left and right inputs, or the LFE input if your sub has it ). Then, you must turn the sub on in your recievers setup menu, and your sub should work.
Try plugging the unit into a clean power supply without anything else on it. I had this problem for years and eventually resolved it by moving the system to a different room that has three power circuits - the sub is now on it's own circuit and I don't have the problem anymore.