Quote Originally Posted by jesse4846
ive never heard an exhaust leak that sounded like a knock before. usually they make 2 different noises.

but based on the OP, he knows his gasket has a huge hole. that would mean its most likely the gasket. replace the gasket and if it still makes noise, you need a motor.
I have heard an extreme leak (basically open dp) that did sound like it had a knock but its the one time that i have heard it.