Viewfinder Frame

So today I noticed that a frame appeared in my viewfinder. I've never noticed this before, and I don't believe it was always there. You can see it disappear when you remove the battery.The frame I'm refering to: (not the grid, but the frame around the focus points)http://www.cameralabs.com/reviews/Nikon_D700/images/Nikon_D700_viewfinder.gifThanks in advance!