Yesterday my exhaust started blowing. After I'd checked it, I found a triangular offshoot from the main pipe, it looks like a small redundant chamber. It's pretty thin and a hole has formed. The rest of the exhaust seems pretty solid though.
Rather than change the pipe, I bought some Gun Gum from Halfords and used it to patch the hole. Seems to be holding up ok and the bike is back to normal. If it goes again I think I'll try and get it welded.