the past few week occasionally i get a single bang when i let the clutch out in gear and the bike is on a hill or under load. I never really noticed it that much because i ride with headphones all the time. Now yesterday on my way home i was on a very steep hill and had to come to a stop. When i let the clutch out to go the bike made this very loud banging noise and the whole bike shook. I was really close to home so I went straight there. I only noticed it when starting off under load. But when i got home i revved the bike up and it doesn't seem to be the engine, the noise seems to come from the left side of the transmission case. Has anybody ever heard of anything like that?