For some reason, a fine vertical line has appeared in the viewfinder. It runs from the central [-] to the bottom of the viewfinder.
If I change the focus point to the bottom one it remains, but disappears on the other 13.

When I turn the power off, it also dissappears.

The camera hasn't had any knocks or gotten wet or anything. I turned the grid on for some shots, and when I turned it off, the line was there.

On a scale of one to ten, how worried do I have to be over this?