Try to turn off AMD dithering. In the AMD software, there is the settings->system tab, you open up the hardware detail, and you will see a 2D Driver File Path.
Go there in regedit, inside the 0000 folder you have to make a "HDMI_DisableDither" dword, and set it to 1. Then restart the pc, and the dithering should be gone. If you dont use HDMI connection you need some different command.