In case anyone is passing through from Google (like I did) with this issue on a Gigabyte Z77X-UD5H (or UD3H), a BIOS update will fix it. You need to use the latest (for me, F16g Beta BIOS). My screen was flickering a few times a minutes, every couple of seconds under load. It was driving me crazy. After the BIOS update, no flicker.