Question On warm-up (see photo): flickering horizontal & vertical bands--what's causing this?

[Hastibe]

These jittery/flickering bands appear when the monitor has been off for awhile (at least several hours, sometimes only after being off overnight), and then go away after the monitor has been on for several minutes. What could be causing this?

 

[Hastibe]

Specifically, is this a monitor issue? Or could this be a cable or GPU issue? (I don't have a cable or GPU available to switch it to, unfortunately, to test.)