supposively theres like some Wiis that were released on launch day that have problems and if you see these kinds of images in MSC when your in megastrike, then you need to go get your Wii repaired.
i guess theres some weird pixels. dont know if its true though. but i think it is since a lot of ppl that reported seeing things like these sent their Wiis to get repaired
its all explained at the nintendo forums. follow the link for full details.