When I was noise tested (by a real exhaust shop) he was telling me that dependent on the type of location they can remove a certain amount of DBA off the reading, light industrial gets 2DBA they can remove, a motorway would mean they have to remove more!Frigging idiots!
I can understand them patrolling and RBTing everything, because we all know after you watch some "car action" te spectators nearly always want to be clowns, so they deserve to be done for speeding and drink driving etc, but they really need to train these coppers up some more on what things are!
I'm glad my car looks stock as (only thing different is rims, and they're a factory size and mimic the factory shape, and no I didn't buy them, they were on the car when I got it.)