What I've tried so far:
- Going back to original drivers, trying current Nvidia drivers and new beta drivers. Clean reinstalls (+ driver sweeper) each time.
- Trying card in a different PCI slot
- Using DVI rather than HDMI cable
- Changed fan profile using MSI Afterburner (doesn't look like overheating to me, temps were just at 53C in the above video).
- Messed around in the Nvidia control panel a bit. Set power management to maximum performance, turned all anti-aliasing to application-controlled.
I contacted Zotac themselves and they ended up suggesting I RMA the card because it was faulty. I sent it back to the original retailer (eBuyer) but they couldn't find anything wrong with it. So I'm totally out of ideas. Anything you could suggest?