My lens has always made a loose kind of rattle/clunking sound when I tilt it back & forth or up & down. The sound seems to be coming from the front of the lens. Just a gentle rocking will cause the "clunking". I've never been sure if this is a normal thing for this lens or a problem so I haven't used it much. I'm hoping it's normal since I bought it used and don't have the original receipt in case I need to send it for repair. Just in case, what is the procedure for sending a second hand lens to Nikon for service?