After installing Ubuntu 14.04 on my ACER V3-572G with a Nvidia Geforce 840M alongside Windows 8.1, I get a small white line flashing (every few seconds) on top of my screen. Ubuntu works fine without any problem and there is no additional driver to install.
I saw people have similar problems but during boot and grub related issues. But I get that line on my desktop screen, GUI.
UPDATE: It happens only if I'm using the highest resolution (1920x1080).