I think a crappy connection is the issue, since it changes as you brake ... it is probably a wire/or connector. go to your car and do a "wiggly jiggly on your RCAs and signal carrying wires.

 

I did a wiggly jiggly on the cables and there was no problems. This is really weird the only thing that makes the bass cut out is just when the car isnt moving. Once the car starts to move everything returns to normal.