I have recently noticed that I am getting some drive chain snatch when getting on the throttle. This is can be heard as a slight clank as the chain comes tight and a bit of a jerk in the movement of the bike. Now the chain has about 4k miles on it and I have checked the slack. It is at about 40mm of slack when on the side stand and the manual indicates it should be between 35 and 45 mm. Do other owners experience this behavior at normal chain tightness or should I put the rear wheel adjusters about it?