Disconnect everything from the back except the power cord. Also put it on the floor and see if that makes a difference (again with nothing but the power cord). if it does make it better, then try connecting one thing at a time to see if it’s one of the cables/casings/connectors that might be vibrating (maybe you already did this, wasn’t clear). Also check that the binding posts on the back aren’t vibrating. Sounds like metal on metal vibration to me but it’s a bit hard to tell from the video. Normal “hum” doesn’t sound like that.