I think the one on the passat is dead. There's a rattle and its not the engine. If I hold the first silencer/cat bit of the exhaust in the engine bay it seems to stop so I think something is rattling inside. Apart from this the exhaust seems nice and tight so I don't think it's knocking anything external to it.

It also drives absolutely fine apart from this.

Do cat's disintergrate? - if so I would have thought it would have made its way out the back by now as its been going on for a week now and getting a bit louder.