Have been down your neck of the woods recently MiniPetrolHead, had a few day's work near Golden Cross.
Driving down with my (much older) mate in the car we came to Cuilfail Tunnel, while he was waffling on I wound down the windows & dropped the old girl down a cog, 'what you doing' say's mate, I said to him just listen to this as we went through the tunnel. Induction roar from CAI, supercharger whine then POP POP POP POP on the overrun
Now when we go any where near a tunnel or bridge he says 'windows down' without any prompting at all

I've converted a Jaguar driver