Either ground loop or faulty plate amp. Try plugging it in to another outlet. Also maybe try it another house if it still hums then plate amp is faulty.
I used to have a really bad ground loop hum. I have 2 subs in my setup and sub #2 has always been hum free but sub #1 always had the hum. I originally thought it was the cable going to my amp. I replaced it and it solved about 80% of the problem. Then I was playing around with the power cord and the hum would stop if I moved the cord the right way. I looked it up and there were guys saying that they broke the ground off of their subs and it solved the problem. I new I had a spare ground bypass plugs lying around so I tried one and it worked.
My Denon AVR doesn't even have a ground pin, neither do my HDDVD or BD players....the only thing that does is my iNuke3K.
I didn't see the video, and I don't know how old that sub is, but if it's really old it could have leaking filter caps.
I'd try a cheater plug like this, and see if it still hums, if it does, the amp has issues, probably in the PSU filter stage, although I could easily be wrong on where the issue lies.
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