I recently upgraded to an EOS 90D specifically so that I could use the electronic shutter, and thus not have to worry about shutter life when doing focus stacks. I am rather alarmed to discover that there is a very definite clicking coming from the camera when it is in electronic shutter mode - sounds somewhat like the shutter operating but significantly quieter. I get exactly the same sound when not in view mode with mirror lock-up. It's definitely not focusing of aperture activity of IS. Does anyone have any idea what the sound may be? Obviously doing focus stacks can wear a shutter - or indeed anything mechanical - out pretty quickly if you do it a lot.