Yes, considered all of those apart from rider hangover etc and tried to assess on that basis but reckon there's somesort of random gereator in there. Certainly isn't final drive chain adjustment!
It's a constant mesh gearbox. The noise is when the dogs on the dog collar, which is connected to the output shaft, engage the slots in the gear you're shifting into. When the speed of the output shaft matches that of the input shaft, the stress in this mating is minimized. I just looked at a used Rocket where the second owner broke the transmission twice by not using the clutch.