Question Lines on monitor go away when changing refresh rate ?

[zerojay]

When I boot up computer my main monitor has mostly vertical and some horizontal lines. They typically go away after a minute or 2 and everything works fine after but I noticed that if I change the refresh rate from 144 (what I keep it at) to 120 they all disappear, but if I change back to 144 they reappear. Any explanations for this?