Lines in an LG 30"

My new LG Slim 30" tube HD set has a strange video problem.  The display works properly for a few seconds and then for a second or two, horizontal scan lines moving upward appear.  During these few seconds, anything moving on-screen appears very jagged and choppy.  It goes back to normal and then repeats continuously.  This happens on all inputs that I can check.  I don't have anything to check the HDMI input with.