I finally got my replacement 100-400 and the zoom ring is stiff but not as bad as the first example. I did not have a lot of time today to use it but my first shot is here: http://www.pbase.com/stewartcclark/image/162910707. The lens still buzzes and I think that it is due to the fact that the lens is constantly focusing without pressing the shutter button the focus tracks. Not sure if I have set something incorrectly in the camera.