Problem with external screen attached via HDMI to Dell Latitude 7480

I'm using a new Latitude 7480 with Win 10 and almost from day one when connecting an external screen via the HDMI, every couple of minutes (sometimes every minute and sometimes once in 5 minutes) the external monitor goes blank for 2 seconds and turns on again.

I can hear the relay clicking.

I've changed the monitor, the cable and yesterday Dell lab has even replaced the whole motherboard in the new laptop and it's still the same.