Are you using native or custom resolution?
Your artifacts looks like hardware fault.
You need to try your GPU on another PC or RMA it.
Similar issue here.
CPU: Intel i7-4790K @4.0GHz (4.4 OC)
Mobo: Gigabyte GA-Z97-HD3
GPU: XFX RX 480 GTR Black Edition
RAM: Corsair Vengeance DDR3-1600, 32GB
PSU: Corsair HX850i (80+ Platinum)
OS: Windows 7 Ultimate SP1
Driver Version: 17.7.2
Displays: Acer X193w (DVI) (No issues)
Acer XF240H (DP) (144Hz) (Many issues)
Issues: Dots on taskbar, not able to pick up in recording.
Screen flickering/tearing during a game of League of Legends, can pick up in recording
Possible fixes: Clean install (no effect)
Updated drivers from 17.4.4 (no effect)
Still have no clue. May have to RMA, see about replacement