Recently I had some time and try to fix it again.
By detaching the display and examining stuff around thoroughly I found out that the camera cable that goes to the screen through the left clutch hinge was worn out in one of its side. I could see a bunch of small silverish wires coming out of it, if that makes sense. First I thought it should be the LVDS/video cable that caused the problem but turned out it's not.
Anyway, as I didn't have a spare cable I tried to fix the broken one by just putting all the small wires altogether and wrapping it around with tape. Since then the problem's gone.
Maybe in the future, I will replace the cable. By the way, to completely replace it takes to tear down the whole display.