The quad bike riders around here have modified their bikes and that includes free flow exhausts (i.e. Baffles removed or aftermarket exhausts).

Also, don't get your hopes up about the police doing anything about the scooter riders. A number of years ago I saw a scooter two up with the passenger wearing just a hoodie. Knowing this was not a good sign I kept an eye on them as my next door neighbour had two motorcycles. Sure enough they tried to steal them. I confronted them and was attacked with a crow bar and a heavy motorcycle chain. My wife called the police in a panic (this was around 9.30pm on a Sunday evening).

The police turned up half an hour later, shrugged a bit and went on their way.