buzzing coming from around b-pipe

[Marshall-P]

when I got to work this mornings blipped the throttle with the door open, and heard a buzzing coming from under where I was sitting, I did it a few more times and there is definitely a buzz, it seems to be coming from my Mugen twinloop b-pipe. I would like its likely to be the baffles can these be replaced and what sort of cost am I looking at?