I would not reccomend using a 3 prong to 2 prong adapter. There is a reason that the 3rd prong is there!
I had a ground loop problem with one sub, which loosening the ground screw would not help. The ground isolator fixed that problem.
When I had two ep500's for the weekend I noticed the ground loop hum slightly came back.
I loosened the ground screw on the second sub and it went away.
So for two subs I need the ground screw loosened on the second one + the ground isolator to eliminate the hum.
It can take a lot of trial and error to finally resolve a ground loop issue.
I would try the ground isolator from axiom- it works great
