I have the same problem with my Hawaii card and my WQHD 144 Hz monitor. It is
not X related and the effect is visible on the framebuffer console, too.

120 Hz setting does flicker like seen in comment 7.
144 Hz setting has a flickering vertical bar a few pixels wide on the left
side, a vertical bar in the center of the screen and overall blurred image.

The OSD of the monitor shows that the input is 2568 pixels wide, has a 214 KHz
horizontal and 139 Hz vertical refresh rate. When using with Intel GPU (which
works correctly) it shows 2560 px, 222 KHz and 144 Hz.

Tried both radeon (linux 4.7.6) and amdgpu (linux 4.8)