nikon 105 mm f 2.8 help
1. When the VR system activates you can usually here a noise (like a low, dull hiss). This is normal.
2. What you are seeing is the effective f/stop. The aperture is staying the same size but the lens elements are moving inside the barrel, changing the actual focal length. This is also perfectly normal and just about every macro lens does it. At 1:1 I believe the largest effective aperture you can have on that lens is f/4.8. Focus at infinity and you'll see that you can open up to f/2.8.