I believe the poster 'magic' has never heard of a dump valve....although at one point my uncle ken did try and tell me that the noise was a and I quote directly 'wind assisted gear change'.
She says she never saw anything, but heard his exhaust as he changed gear and wants him to be banned. Saying that, I wouldn't buy a car of him if he drives around everywhere using 1st and 2nd.
As for you unclemunkl, he may be an unsafe driver but you need english lessons:
"Now doubt he will now face the normal 50 pence pence fine and three points on his licence!
I say jail thre idiot and make the roads safer for the rest of us!"