Canon USA has issued an official response to the 5D III IS noise issue:
“We have acknowledged that when using the camera with specific lenses, there is an abnormal noise during IS operation when the shutter button is pressed halfway (or remains pressed halfway), and we are now considering the countermeasures. We will let you know about the countermeasures as soon as they are finalized”
The two affected lenses are the Canon EF 200mm f/2.0 L IS USM Lens
and the Canon EF 800mm f/5.6 L IS USM Lens
Note that image quality is not affected by the abnormality. Also note that this noise does not occur during Live View including during video capture.