Wierd problem and it is intermittent. It is not a ground loop since it still occurs when the sub is not connected to the system. You should call 1-866-244-8796 and talk to the customer support staff or one of the engineers to see what they have to say about this issue. I suspect there might be problem with the amp. Keep us posted.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne