Start by trying a different cable. You can also try a few different resolutions to see if a lower resolution at the same refresh rate has the same issue. That will tell you if it is a bandwidth issue or the panel having issues with fast refresh.

As for RMA, I would start with the retailer if possible since they will swap it out for a new one. Otherwise, yes just contact ASUS support to setup an RMA for repair. Make sure it is reproduceable, otherwise they may plug it in and think everything is OK.