It starts when I open a window or a program, but when I minimize it it stops or becomes almost non-present. It is not all the time though. The problem is that I don't know if this is a problem and should I be concerned? Never mind, I found a simple thread on another forum and one of the replies sugested it was from improper refresh rate. And that was exactly it. Few days ago I played GTA: San Andreas and it usualy changes my screen refresh rate to 60 hz but I forgot to change it back to 85 hz. Problem solved, thank you for this forum.