FAQ: Is the Canon EOS 1D X
affected by the Canon EF 200mm f/2L IS and EF 800mm f/5.6L IS Service Notice Regarding IS Noise
Canon has not released an offical statement regarding this issue, but I can tell you that my 1D X attached to my un-corrected Canon EF 200mm f/2.0L IS USM Lens
produces a normal IS sound.
Roger at LensRentals.com confirms that the several Canon EF 800mm f/5.6L IS USM Lenses
he tested on a 1D X also produce a normal IS sound.