I'm still very happy with the picture quality and versatilely of the 52B630. At the same time I'm amazed by the newer sets in the same category, 60 inch LED sets at only two thirds the price I paid for the 52B630. The point being that I wouldn't spend too much time and money trying to fix this set, I'd look into getting a new TV.
Nope, not 'mute' related. Just sometimes will play the tune, sometimes will not. I have not been able to come up with any specific condition that causes the tune to play or not to play. Just seems random.
If it doesn't play the tune it isn't something I would worry about. Now that I think about it I am sure there have been a few times mine hasn't played the tune either. Its not something I'm going to worry about. It could be worse, we could be having those dreadful HDMI connection issues.