I just saw in another Legal Issues post you submitted the statute used around here for modified muffler cites was quoted in 316.293 (5)b FSS. No need to post my pics because this is the exact same thing I saw in the 2006 book.
(5) NOISE ABATEMENT EQUIPMENT MODIFICATIONS.--
(a) No person shall modify the exhaust system of a motor vehicle or any other noise-abatement device of a motor vehicle operated or to be operated upon the highways of this state in such a manner that the noise emitted by the motor vehicle is above that emitted by the vehicle as originally manufactured.
(b) No person shall operate a motor vehicle upon the highways of the state with an exhaust system or noise-abatement device so modified.
Kind of general, so it covers anything "louder than factory".
