The thing with vehicles with modified exhaust systems is that the riders/drivers are often the same people who ride/drive like a$$holes. Rev the crap out of it at a stop light, accelerate fast, rev to the redline or pass you on the inside on the 401 at 170 - 180 kph. They also specialize at doing all of the above at 2 in the morning.
I have no problem having these nice and considerate folks stopped and ticketed. Part of the process should be a follwup inspection where the owner has to return to an inspection station in a week to validate that the illegal exhaust system has been removed and replaced with a legal one. Don't show up, then police drop by the residence and seize the plates. You're never going to solve this issue unless the law has some teeth and costs the owner money.