How are your temperatures?
Have you checked you don't have one of the reference design models, some of which have a malfunctioning cooler and will be replaced.
If it was during video playback, try changing angle graphic backend -setting from edge://flags/ to OpenGL and disable video hardware acceleration from everywhere you can.
Could be a monitor or monitor cable issue too. Try connecting with a different cable, from different output to different input and perhaps to another monitor or to a television instead of monitor, for testing.
Could be that files become corrupted for some reason, like memory speed or timings too tight or some other issue. Maybe scan for corrupted files in system.
