Okay, new development. It is definitely a ground issue! I put the ground screw back in all the way and low and behold, the continuous vibration stopped immediately. yay for me, right? NOT QUITE... put in the a movie and sure enough, when a scene big rumble scene came on... the drivers continued to rumble even though the scene was done and there was just dialog going on.
And when there was a large thump in a scene the drivers thumped continuously in rapid succession...
When I loosened the screw, those issues stopped but, you guessed it, the continuous vibration was back.
Maybe if someone from axiom reads this they'll be able to give me some other ideas before going on my road trip.
