same problem here. seems like XFX haves very poor GPUs. i sent one in because of black screen bricked. they sent me an XFX RX 470 and is doing exactly your problem. starts flickering and pixelating everything.
ok found out after a complete format and reinstalling everything. seems like the Curse Voice app overlay was making the GPU go crazy. uninstalled the app and restarted. played a full game of heroes of the storm and no problems for now. also updated my bios and everything. but the flickering stopped after uninstalling the app. maybe you have some overlay software confilcting to