It seems that even though your exhaust passes all noise restrictions and emissions requirements, you get the ticket because your exhaust system is coated with shiny silver "stuff". They want you to have the rusty, corrosive material that came with the car. It's purely a cosmetic and visual issue in most cases, unless you have no cats and you car is really too loud, in a legal sense. I wonder what would happen if I put on the OEM muffler but still had gutted pre-cats with no cats at all? Would they stop you for the noise, though everything visually looked fine?