Thread title immediately made me remember something.
Loudest exhast I've heard?
I used to work at a motorcycle workshop in Ellesmere Port. They once had a Yamaha XJ1300 (retro looking motorbike) with a straight-through system, to be set up on the dyno. No silencing at all. THAT was bloody loud. The dyno was housed inside a soundproof room. With a normal race bike running at full chat on the dyno you could just about have a conversation outside the dyno room.
This Yam was so loud, it hurt my ears despite being stood outside the soundproof cell, with ear defenders on.
Flipping Brilliant. No idea how the guy managed to ride it anywhere without getting stopped.