Ok, update... I removed the cable tv wire from the wall. Instantly got some weird feedback through the sub. I tightened the ground screw back in and everything went quiet. Since I had a Monster Power Home Theater PowerCenter Surge Protector, I decided to run the cable tv through the power bar since we didn't try that. Everything looks like its working fine and the sub is quiet like I expect it should be.
Although everything seems to be fine now, the sub still doesn't go into standby mode. Even when I disconnect the sub cable leaving only its power cord plugged in, it still refuses to go into standby. I'm assuming its still picking up some kind of interference from the electrical wiring in the house.
If anyone has any last suggestions, I'm all ears. I'll call Axiom tomorrow and see what they say but otherwise, I may have to deal with turning the sub on and off every time I want to use it.
