My cats sound like a box of rocks. It isn't (unfortunatley) the heat shields, it's the material inside. When I bought the car it had off road pipes, but I had new cats installed to pass inspection. They lasted for about 6 months until the material inside broke up. The company covered it under warranty. Now it's doing it again and they won't cover it again because they said it was a fuel issue. So a couple of questions for you 5.0ers.....has anyone ever tried breaking up the material inside? Not exactly legal but it would work to pass inspection, kinda like stealth off-road pipes. Anyone have any idea what might cause this? Thanks, RJF