I thought these cars had 2 cats - one on the dump pipe and another between there and the muffler.

Blew a hole in the second 'cat' the other day, called the local exhaust place for a chat about fabbing something up. He reckoned it's not actually a cat, rather it's a resonator.

Is he right? And if so, is the exhaust going to be noticeably louder if I just bolt in a straight-through piece of pipe (got a stupid loud cannon on the end) ?