External monitors are flickering on a T520

[Frankie]

Hi everyone. I tried to plug a VGA and a newer Displayport monitor on my T520 and both flicker occasionally, especially when doing operations on a browser for example. When I'm watching a movie or TV, the monitor stabilizes. I have a Nvidia NVS 4200M with drivers up to date and Windows 7 64bit operating system. I tried to change the refresh rate and it didn't solve the issue. Do you have any idea of what is causing this?

Thank you
Frankie

Edit: I have noticed that if I make my external monitor the main display the flickering/blinking disappears! But I want the laptop screen to be the main display. This seems to be a Windows 7 issue or a video card software issue, it's very peculiar and annoying.
Edit: My mistake, it still flickers when external monitor is the main display. Sometimes it does, sometime it doesnt.