If the sound bar works the cheapest fix is to unplug the TV speakers. To fix it my bet is the board or boards that drive the speakers.
I own the Vizio SV420M 42 inch television. I have had it for about 4 years. It has been a great tv. About a month ago, when I turn the tv on on random occasions I will hear a static noise coming from the tv speakers. I turned the volume down on the tv all the way to 0, and the static is still heard. It is loud. It only stops if I turn the tv off and on again. The static sound will then go away, until I turn the tv off for a while and turn it back on. I have checked all cables, took them out put them back in and nothing helps. I have the Sony HT260H sound bar hooked up to it using an optical cable. I also have a PS4, direct tv receiver, and x box 360 hooked up using HDMI cables. I have been searching online for a month now, with no help. I have contacted Vizio support, and all they could tell me is it's no longer under warranty and they give me numbers to tv shops. I don't want to take it to a shop if it's an easy fix. Please help!!!