Well not as such, but thats what it sounds like..

Basically a friend had a new backbox and mid section fitted to his ford escort 1.6 mk6 at the weekend, about 4 months before that he had a new catalyser put on it.

Since he has had the new mid section and backbox put on, when you rev the car up it starts popping and banging, and then pops and bangs as it comes down the revs?

He took it back and there is no leaks, checked the CAT the cat is working fine, and we aswell as the exhaust place are as confused equally as to why its doing it?

The car runs fine, drives fine, just its popping and banging on the exhaust?

Any ideas?