I just received the lens and started playing around with it and immediately noticed that when the IS is turned on, it makes a clearly audible "whirring" sound while focusing and for 2-3 seconds after focus is locked. When IS is off, no "whirring" sound.
I have several lenses with IS and I've never heard anything like this. Is 2-3 seconds of "whirring" normal for the 300mm 2.8 IS?
Would appreciate any feedback since I'm in the return window....thanks.