I have a new XFX RX 480 8 gb card that had been working just fine for about 5 days on my BenQ 2k 144Hz monitor. Just today I stepped away from the computer for about an hour and came back and the text was really fuzzy and there was a subtle flicker on the screen. My 1080p secondary monitor looked fine.
I tried a different cable with the same results. I plugged in my old Nvidia 660 ti and the monitor looked fine so I know it's not the monitor. I tried clearing all the drivers and reinstalling to no avail. It almost looks better on the default windows driver and gets worse when I install the new drivers. Nothing changed when I walked away and it was working that I know of.