This is by design for G-Sync, and is not an issue with the video card. Under some conditions, you may encounter a brief flickering on some monitors with G-Sync enabled. The flicker happens when the frame rates momentarily drop to zero, such as when you take a screen shot, entering a menu, or when background content is loading.

The flicker occurs when the refresh rate of the monitor drops to zero to match the frame rate. A zero refresh rate causes the pixels to fade to white. To prevent this from happening G-Sync is designed to force a refresh every so often. The flicker seen is this forced refresh of the screen, bringing the fading pixels back to the proper color.

On a non-G-Sync display with a fixed refresh rate, this is is not an issue, as the refresh rate never drops to zero.