Whit “water off”, on the “islands” map ive seen the ground outside playing area flickering. Can be seen also if you dive underwater whit right ALT.
This occured for V40 & previous versions for viewing underground with restricted camera OFF (right ALT).
On my previous DELL laptop, this behavior occured very infrequently but once it started, it would continue until I quit & restarted the game. On my new DELL laptop, this behavior occured on ALL mapboards ALL the time — until I turned off the OpenGL extensions option. Disabling this option paints all underground areas as black & solves the flicker problem.
In fact, I so much liked the contrast of all black for all underground views, that I was OK with disabling this option. I don’t know how many other graphical features I disabled — none that I readily noticed — but it removed the flicker AND improved the contrast between aboveground & belowground views so I was happy.