[Wisconsin_Snake]

I am guessing that you have the "old" style side pipes. The old styles pipes have two internal 1 inch pipes to help silence the car a bit. So from the header to the side pipe, there is a round plate with one, 1 inch inlet going to the first pipe... On the other side there is a plate that connects to the second 1 inch pipe.
I am guessing that one of the pipes has disconnected from the plate. Or the plate has separated from the pipe and the external housing of the side pipe.

The up side is when you replace the glass pack portion of the side pipe, you will free up ALLOT of HP.