Second monitor flickering gently

When I coected my 22" Asus monitor to my laptop (at 60Hz refresh rate) via VGA cable, monitor started flickering gently (very visible on darker surfaces(colors), like grey or something like that, not so much on lighter colors, white etc.)

And I have 2 graphics cards on my laptop (laptop is Samsung NP300E5Z, intel's i3, 4gb ram):

• Intel(R) HD Graphics 3000
• NVIDIA GeForce GT 520MX

VGA cable works (I tested it on my desktop computer), I updated all drivers, any suggestions what to do next? I thought that getting HDMI to VGA adapter may solve the issue? Because my laptop can also accept HDMI cables, or changing the refresh rate? (but my computer wont allow me to change it beyond 60Hz, only 59Hz and 60Hz options available)

Thanks