So, as I took the engine out I found the source of the rattle that had plagued the car.................
bodgers! Lovely! the flange has been cut off the rear of the cat and the flange from the exhuast has been left, cut off, on the exhuast
In the photo it looks like the flange is welded to the pipe but trust me, it isn't/wasn't!
Yes, that's right: the flange is quite free to move up and down the exhuast pipe. I have the name of the company that did this but obviously won't publish it here or ever go to them for work in the future. Muppets!