Knock Knock

[sanoke_imp]

Let me expand on my original suggestion. The front sprocket has moulded on rubber dampers on both sides of the sprocket. The chain body rests on these as it turns. When the sprocket has worn, these will hold the chain up a little so the roller doesn't rest in the tooth valley of the sprocket when the engine is not engaged. This allows the roller to move forward, contacting the back of the worn tooth. The following tooth then strikes the following roller and slips forward making a knocking noise that sounds like it's coming from the transmission. I've seen this before on other bikes that have the same kind of sprocket. Lubing the chain will often make it go away. Sometimes adjusting the chain helps too. Just give it a try next time you notice it. It really isn't anything to worry about and it will stop when you replace the chain and sprocket.