ATEM Mini Pro Noise

I am getting noise across the screen from a MacBook laptop, through the ATEM Mini Pro, on the monitor on the HDMI output. Looks like small white dots.
If I take the ATEM Mini Pro out of the system (ie, use the same cables and a HDMI extender to connect them) then there is no noise.

white dots across the screen, and the blotches on the grey window.

Russ Baker ATEM Mini Pro Noise_1_small.jpg (675.93 KiB) Viewed 516 times

white dots across the screen, and the blotches on the grey window.

Russ Baker ATEM Mini Pro Noise_1_small.jpg (675.93 KiB) Viewed 516 times

First thing I would suggest you do is to verify that the display input resolution, ATEM resolution and computer output resolution match in the off chance you might be getting scaling artifacts of some kind.

What happens if you turn off Mirroring?