I have recently upgraded to Ubuntu 18.04, and I am experiencing subtle (but constant and rather annoying) screen flicker. My computer is an HP Envy x360 Convertible 15-bp1xx; using Intel graphics driver. The flickering is not specific to any application, but it is more visible in large medium-gray areas (e.g. applications with dark themes, desktop backgrounds, etc.)
I just ran into the same issue. Was fixed by changing the refresh rate to 59.96 or 59.93 (it was on 60.01) - no clue why. Just opened display settings and fiddled around after reading much older posts on similar issues.
Hope this sorts it out for you!
I had to edit my monitor config and change the framerate. By default mine was set to 60.169086456298828.
open terminal and run the following:
sudo gedit ~/.config/monitors.xml
edit this line:
set it to be lower than 60 as mentioned by 4levels, I used 59.96.