Fixed my group loop problem - added a MonsterCable surge suppressor with the Cable surge in/out, it immediately cleared up. I'm pretty sure it's a ground loop between the cable signal and the power outlet. Once I had them all on the surge supressor, it probably put them to the same ground - 60 HZ ground loop immediately disappeared.

People only see it on their sub because generally they have their crossover set to 80 Hz or higher.