I knew there was a problem with the exhaust system before I gave the car to my friendly mechanic for him to get it through the MOT. It had been rattling quite badly, obviously from inside, and the engine was not running properly. As you can see from this post I had changed the rear mount from solid to a rubber mount. It now looked as though the extra vibration had loosened off the baffles.
When he took it apart it turned out to be the catalytic converter that had disintegrated and parts of it had gone into the silencer and that was causing the rattle. The good news was that once the bits were removed the silencer was fine. We knew this was a non-standard cat so both of us went on-line to try and source a new one. And we both lucked in. He found one at his local supplier and astonishingly, I was offered a complete exhaust system by another member of the RHOCar club. I just had to pick it up.
So, having previously bought a manifold I now have a complete spare exhaust system. I think it might be time to redesign the system by adding a flexible joint between the manifold and the exhaust system and mount the can at both ends, thereby isolating it from the engine vibration.