It could well be the built-in orientation sensor. This is known to make a slight sound when the camera is tilted. Nothing to worry about
BrianWelsh NikonianCheck out the Nikonians Team pages
Copyright © Nikonians 2000, 2013
All Rights Reserved
Nikonians®, NikoScope® and NikoniansAcademy™ are trademarks owned by Nikonians.org.
Nikon®, Nikonos® and Nikkor® are registered trademarks of Nikon Corporation.