On my firebird the weld between my cat and intermediate pipe has totally broken apart. When i start the car it sounds like there is a knock on the passenger side but the leak makes it to loud for me to hear it. Is there any way the leak could be responcible for making the engine knock?

 

does it still make the noise after the car warms up?

 

Take a stick of wood,2X2 works good, about 20" long (doesn't have to be 20", just don't stick your head in the fan). Start the engine, place one end on the engine near where the knock is suspected, and the other end on your ear. If it's knocking you'll hear it.

You can change the place on the engine to find the closest point to the knock to pin point also. Just don't let the neighbors see you, they might think your crazy.

 

Oh wait i wrote this late last night i mean the weld between the Y-pipe and cat broke.