Sound going out on 52''Sony?

I have a 52' Sony Bravia LCD.For two years the sound would go out and I thought that the DVR box for Comcast was the problem after three boxes and new cable in to the home I still have the sound going out.I will be watching something and the sound goes out for about two minutes and back on this may happen every five minutes .When I change channels the sound comes back and the sound on that channel will go out and i have to keep changing channels to keep the sound.Does anyone have an idea what this could be.Does this sound like it could be the TV. Are there any Sony Techs that could give me an answer.The TV is about three years old.