Exhaust Noise

[McMouse]

Automotive engineers have perfected exhaust silencing to a point where some powerful cars just whisper past. However some super-sports cars have specially tuned exhausts to provide their trademark howl or roar. This is ok for the track but hardly suitable for the high street. When I was out earlier today a Ferrari revved away from the traffic lights and could still be heard when it was out of sight half a mile away. Why is this tolerated?