Canon EOS-1D X Mark III Advanced User's Manual page 901

Sensor cleaning problems
The shutter makes a sound during sensor cleaning.
Although there is a mechanical sound from the shutter during cleaning after [Clean now
] is selected, no image is recorded to the card (
Automatic sensor cleaning does not work.
If you repeatedly turn the power switch <
period, the < > icon may not be displayed (
).
> and <
).
901
> within a short time