As a Christmas present for myself (bit expensive to be from anyone else!!) I just got a 400 5.6L prime. I'm slightly concerned by the noise it makes when focusing, which is an electronic whine with a slightly metallic edge to it.


My other L lenses - a 24-70, and a 70-200 f2.8 IS - are completely silent, except of course for the barely audible sound of the focus mechanism changing direction as it searches for lock and the IS whir of the 70-200.


I know that the 400 is a much older design than the other two lenses so maybe the technology is slightly different - is this noise normal?