Can you clean a catalytic converter.
I do not have one on my car currently i am about to put on one replacing the poorly made dacat pipe

Can you cleans these and what with also will it make a difference to my MPG re fitting the cat.
And will i lose any power removing decat pipe i will be replacing the decat pipe whatever i just want to know if it will run differently and it because of the cat and nothing else doing a lot of work to it this week this being the main thing.
Does any one know how loud my car would be with the middle box removed i have a after market system on there and it doesn't evan make a noise at the moment like a standard exhaust just want a little noise with re fitting the cat im hoping for a small noise increase really.