Black Sqaures and frequent crashes

Hi,

I've experiencing graphical glitches usually followed by a game crash in the last weeks. After some time in game I suddently get black (if I'm in 2.0 territory) or white and yellow (if I'm in Heavensward territory) squares flashing all over my screen and, usually after some time, a crash.
The squares look like this: http://imgur.com/a/0EfDl
I have an Intel i5-4570k, 12 GB RAM and an AMD R290X as graphics card. My OS is Windows 8.1 x64.
I just updated my drivers to the latest version and the temperature of my system is in the green area. Also i don't have any problems in other games and checked my VRAM for errors.

What I tried in game so far for resolving the problem: I switched every graphics setting up and down one by one and waited until the glitches appeared again and switched between dx9 and dx11. Couldn't pinpoint the problem so far.

Has anyone an idea what could cause these glitches and crashes? I'm thankful or any help :)

Is your GPU overclocked? This issue look to me, like too much OC or a corrupt GPU memory.
Please take a look into Radeon Settings/Overdrive to check if there is anything turned off.
Did you remove the driver via the DDU Tool?

If nothing helps, i would contact GPU manufacturer for RMA.