At some time you had speakers that weren't magnetically shielded or some other magnet near your screen. You need to get it de-gaussed which is basically bringing a large electromagnet near the screen to make the whole shadow mask behind the glass of the tv not have magnetic hot spots.
A TV shop can do it for you, or you can rent a de-gausser which should come with instructions.
And this is a Mac forum, there are forums for hacking and fixing Sony TV's. Use google to find them.
drewman