1994 Dodge Spirit sounds in the doors

We just purchased this car and had a tune-up and new muffler and some gaskets replaced and oil change. The previous owner had tried to put in a new radio but never put it in. The radio and speakers have just the wires inside. The weird thing is when we touch the brakes we can hear a tapping inside all the doors. When we touch the window lock button (which don't work) the tapping stops. How are these connected the brakes and windows? What might it be?