Busted Cat-Coverter

[Nismoman240]

I think I got a busted cat cuz my 240 makes a bad vibration sound from the exhaust I don't know if its punctured or what, Im gonna be getting a new cat and exhaust from a friend but i kneed to know what diameter piping is best, its a non-turbo 1995 so Im thinking about 2 1/2 or 2 1/4? Plus whats a good muffler?

[Red coupe]

its probably just your heat shield rattling against the cat....

Most people seem to prefer a 2.5 size exaust but some argue going as high as 3inch can be benifitial on an NA If you dont mind the noise...