I have standard exhaust apart from prodrive back box on 02 wrx sportwagon.
It's just developed a popping sound particularly when hot.just wondered if anyone had had same problem before I get under car at weekend sounds like it is coming from front of car.what's the deal with how many cats you have to have for mot.also reliability issues if removed which ones better to remove.cheers

 

Blowing manifold or header gasket i reckon.