Faint horizontal lines across screen?

I recently purchased an iPad Mini and I noticed that it's got very faint horizontal black lines running across the display. They're really only visible when holding the device in portrait and even then only along the upper portion of the display. Of course that's exactly how I hold the device for reading.

Anyway, at first I assumed this was from the lower pixel density of the Mini, however my wife has a Mini as well and her display doesn't appear to have the same issue. Has anyone else experience something similar? I personally find it annoying but I'm not sure the problem is pronounced enough to warrant a repair.