This is because you have something emitting an electric magnetic pulse close to the TV. Like a large unshielded speaker or large Battery. First thing you need to do is move anything near the TV away and see if that correct the issue. Next would be to degauss the TV. Unfortunately the TV probably does not have a built in degausser.

A degausser is an electro magnet in a circle. you plug it in and run it around the surface of the TV.