What a great forum! Thank you for all of the suggestions and for the reassurance that I won't damage the lens. The "clunking" did stop when I turned off the VR. Since I have been using very fast shutter speeds, I will try turning off the preflash and using the flash to catch the hummers in mid air. Great detail in the hummingbird photo too. Thanks again to all of you for being so generous with information and so rapid in answering.