CAR AUDIO STATIC Through car speakers not subs?

I would have to guess that there is probably a loose connection behind the deck that is causing the static. When the car moves, the wires probably move around where the connection is and that's what gives you your static. It could also be that bare wires may be touching together behind the deck and that can give you static through all the speakers. Either way I would just check all the connections in the dash and wrap them with electrical tape to make sure no wires are bare. In the case of the subs, I'm assuming they are wired directly to the head unit and they would be on an entirely separate connection than the speakers and that is why you don't notice interference in them.