Plus I'm pretty sure it would be pointless recording the noisy bollock whizzing up and down my road on his motorbike, because apparently number plates are optional when there's fuck all police about.
It's the inverse - the car is quiet for just one day, its MOT day. The owner will put the standard exhaust on for the MOT, then put the loud one back on once they have the MOT pass certificate in hand. Same thing with numberplates with odd spacing to make words. The owner will put a standard plate on for the MOT then swap it for their illegally spaced one once the MOT is done.