Are you on digital tv? At first it sounds to me like its an interference of some sort, which won't be the television itself but your digital line.
If that's not the case then I suggest plugging the tv into a dvd player or game console and see if the problem continues. If yes, then it is the tv and may need repairing. If no then it's something to do with your digital provider.
If that's not the case then I suggest plugging the tv into a dvd player or game console and see if the problem continues. If yes, then it is the tv and may need repairing. If no then it's something to do with your digital provider.