Thanks for your reply. Being a neophyte I was sure it was something I was doing. I am using the AF-ON and tried it with both AF-C on and off with no observable difference in the amount of shuddering that occurs. I have read that for action shots other photographic equipment combinations are better than the D800. However, the amount of clunking and shuddering that occurs is directly proportional to the size of the subject I am trying to focus on with this lens. So I will try calling Nikon for their input as well. Thanks again.