Speaker hum from Subwoofer

Well, that's interesting, Luxman has gone to using a grounded AC socket, and no longer carries the double insulated label. 

My Definitive Technology sub stopped humming when I moved the plug to a different outlet that’s on a different circuit. Worth a try if it's feasible.

Possibilities:

- If the sub is plugged into a different circuit, plug it into the same one as the Luxman. (Same circuit not same outlet.)

- Are any of the interconnects unshielded. Check routing to make sure they’re not crossing over a power cord,

- Disconnect any non-audio components from the system - such as TV, computer, gaming console, etc.

Try a cheater plug and see if that resolves the problem. If it does then you will know that a ground loop is causing the hum!