Now going to replace the cat as it seems to have gained a loose stone inside it - any thing to look out for? Never done one before so any help welcome

 

Remember that the old cat has platinum inside it, do not let some 'helpful' person take it off your hands for nothing.
Is it falling apart inside?

 

Sounds like a load of nuts and bolts loose inside a steel pipe, which I guess isn't too far off really. Car just passed its MOT (UK) before it got too noisy so as it runs ok there is no particular hurry, its just a bit embarrassing sitting in a soft top with a loud clanking coming from underneath people look a bit puzzled