Knocking noise from exhaust

[zkerzner]

Hello everybody, 2 days ago I was on a ride with my zxr 400 1997 and I stopped for a drink in our shopping center, when I came back to my bike and started, it suddenly started making knocking noises from middle part of the exhaust pipes, when I rev it a little bit it gets faster, I tried to look at headers tighteners and they were slightly loose, so I tightened them and it continued making those noises.
Every ideas are welcome.



(Sorry for my English, I’m from Europe)