Mine has this issue also, notice it the first day while adjusting the chain. Now that it has a little over 2000 miles on it is more pronounced than it was then. Checked 2 never ridden ones at the dealership and they both had the up and down play to about the same degree mine had originally. Definitely in the dog bones. Once it gets to the point where I feel that it's a safety issue, if it does, I'll take it to dealer and let them deal with it while it's still under warranty.
I had the same issue once with a GPZ 1100 but it really never became a problem.
