I think you have a fly or other insect in your monitor. This has happened to me before when my apartment had some fruit flies. You can...
1. just hope it dies off screen
2. turn your monitor off to prevent its legs from getting stuck to the panel. When it dies hopefully it falls to the bottom.
3. go crazy like I did. I duct taped folders and sheets of heavy paper all over the front of my lcd so no light could get in. Then I put it in a dark closet and shone a lamp through the vents on the top. I was hoping this would attract the insect to the back of the monitor. I left it for 36hrs, and when I came back, there was no more fly. Good luck.