Before cutting open any devices or cables, does the sub power cord have a ground pin? If so, can you find an extension cord with only a 2 blade electrical plug, meaning one without a ground pin?

I have had humming issues with all 3 Axiom subs I have owned, and the ground screw fix did not work with any. All were fixed by the above.

Your mileage may vary, but it is easier and safer than some of the above suggestions.