Video of the "knock"? If its had the same noise for 6k miles its probably just a louder engine and I wouldn't worry about it. If the noise got louder or something recently, that sounds like cause for concern.
Me and my brother have the exact same bike, his with 14k on it, mine with 6k or so on the motor. Both motors are 07's. Mine sounds much more tickey than his, really worried me at first. Now I just dont care. I'd actually say mine runs better. loud motors man.