Somehow my DisplayPort cable is broken in a way where it makes flat surfaces look like they have a texture. It still displays an image, the image is just not correct obviously.
And I thought digital signals would prevent this kind of stuff. Guess not.
Weird problems require creative solutions. One of the problems was the fact that the graphics card sits a bit too high in its slot, which means the output ports were slightly obscured by a metal part of the case. A part which may or may not be visible in the picture... 
It solved the weird noise problem, but the cable still seems to have a broken end that causes the display to lose connection, so I guess I'll have to get a new one.
Thomas Frans 🇺🇦