I have a very peculiar issue with my Wii.
I have just bought an official power adaptor and a composite cable (third party but gold plated).
When I am playing Skyward Sword the picture is fine except for when a loud sound is play through the game. For example, if I swing the sword and kill an enemy loads of horizontal lines will dart across the screen in time with the sound and then disappear as soon as it goes away. Similarly if there is a dramatic scene or event that happens that creates a lot of noise these lines will occur again. I have no idea what is causing this. The lines are soft horizontal lines that are fuzzy and distort the picture. It only happens with sound. I have tried muting/removing the sound cables but that makes no difference.
I am stumped as to what the issue is. My TV doesn't have this issue with anything else.