I've been having a similar issue. But it's only in the Wii Menu. Once I load any kind of software everything seems to correct itself And there are no display issues.
I will turn on my Wii with the component cables connected. Whenever I use the cursor to select things with my Wii remote, The picture gets all choppy. Sometimes the image turns completely blank. Sometimes when I boot it there is no image at all.
Maybe I just need a new set of cables? I dunno. But it's only a problem in the wii menu. As I said, everything works fine when software or homebrew is being displayed. The image never cuts out then.