My vizio tv model vw46L gets a gradient black box

My vizio tv model vw46L gets a gradient black box covering about 1/2 of the tv screen (left side) sometimes it lasts for a few seconds or a few minutes. It only happens every now and then (5 - 10 times a week) I have tried unplugging it and resetting all settings from the menu, but that did not help. Thanks in advance for any help....Sincerely Frank M...... P.S The one year warranty ended in July