1999 Yamaha Fazer 600 rattling / tapping noise / cam chain / blowing ?

[His Dudeness]

Sounds like an exhaust leak to me too. My exhaust looked perfect no rust anywhere but it had rusted behind the clamps and all four had to be welded. Like unfazed said be really careful with the nuts and studs. They're too small imo they should be M8 and the nuts should be closed at the top not open. Make sure you use plenty of penetrating fluid and work the nuts back and forward to clear the crap out of the threads.