Flickering pixels on monitor

[geertsch]

I use an extra monitor Acer G277HU to my Imac 27 inch 5K. On the extra monitor i see tens of flickering pixels.
When i link it up to macbook pro (also via HDMI-tunderbolt)...the imag on the monitor is perfect.
I tried changing resolution....color profile...rescaling but noting works.
Can somebody solve this problem?
many
thanks
geert

 

[maflynn]

Sounds like maybe the iMac is having problems driving the other monitor

What GPU does your iMac have?

 

[geertsch]

I use an extra monitor Acer G277HU to my Imac 27 inch 5K. On the extra monitor i see tens of flickering pixels.
When i link it up to macbook pro (also via HDMI-tunderbolt)...the imag on the monitor is perfect.
I tried changing resolution....color profile...rescaling but noting works.
Can somebody solve this problem?
many
thanks
geert

[doublepost=1476534812][/doublepost]LEGEND
iMac5K M395X = 'late 2015' iMac Retina 5K 4.0GHz Quad-Core i7; Radeon R9 M395X GPU (4G GDDR5); 16G RAM; 1TB flash storage

 

[maflynn]

You have the high end dGPU, so there's no reason why it can't drive both of them

 

[997440]

Eject and remove any attached peripherals, if applicable, to see if there's any improvement.

If you haven't already, use the same mains supply when testing both scenarios to eliminate the possibility of line "noise" as a cause. Also consider any power strip, UPS or other extension product that's between the machine and the mains.