Sorry, I haven't been clear enough have I.
This problem occurs when there is a light area next to a dark area, the edges of the 4:3 mode are just an example I chose. It can happen anywhere on screen and in any mode, video source does not affect it either.
I made the graphics myself and used Monkey Ball to illustrate the problem, it's from the web although I do own it aswell.
You can adjust the 4:3 mode in the service menu. If you haven't used this before make sure you read about it, and write down any settings before you change them.