Slow shutter sound on Canon 5D Mark IV when using off-camera flash

[daveburt98]

I've been using a Canon 5D Mark IV for work now and it's a solid and reliable piece of kit, but recently I've started noticing an issue when using off-camera flash.

When setting up a 600EX II-RT speedlite off-camera with a PocketWizard Flex TT5, I've notice a strange shutter noise almost every other frame I take. It's difficult to describe and I can't seem to find anyone else talking about it, but it causes some weird movement being registered in the final image and it results in poor image quality - fixable in post but still not ideal. The only way I can describe it is that the shutter almost sounds delayed, like a mirror lock-up sort of sound, but then for the frame or two after, it sounds completely normal again (fast and snappy). This obviously is quite annoying and confusing, especially as it's resulting in me over compensating by shooting more frames than I need to. Weirdly enough, it never happens when the speedlite is mounted on the camera, so I'm suspecting this could possibly be related to the PocketWizard itself as opposed to the speedlite; some potential delay in transmitting the signal to the flash?

Does anyone know what this could be/has anyone experienced anything similar?

[p4pictures]

If the problem doesn't exist with the Speedlite on the camera then it makes sense to lay it at the door of the PocketWizard. 

Is this new sound only happening since you used the PocketWizards, did they ever work without creating the same shutter sound?

Have you updated the camera firmware or the firmware in the PocketWizards recently?

If you have a pair of 600EX II-RT units or a Canon ST-E3-RT transmitter can you try using that off-camera and see if it creates the same sounds?

Just a thought, are you shooting tethered in to EOS Utility with Live View window open, or using Live View on the camera? In live view the first curtain is open, so when you take a shot, it needs to close the curtain and then reopen to take a shot and trigger the flash.

[daveburt98]

Good point about the firmware, I'll get this updated and see if this fixes anything! You're right, it is only when I'm using these PocketWizards...
Unfortunately, we don't have a spare 600EX II-RT unit in the team but could be an option for me to look at the Canon ST-E3-RT transmitter if the firmware update doesn't solve anything.

Not shooting tethered, this happens mostly on location, but I do see what you mean about the sound that the live view mode creates - it's different to this and sounds exactly the same to the normal shutter sound but with a 1/2 - 1 second delay between the shutter opening and closing.