If you want to test I would go rent another copy first. If it does the same then you have an issue and hopefully your Wii is still under warranty. I had the same problem and noticed it while playing Rayman Raving Rabbids. This was only during scenes with fog or very dark background. The problem got worse. I created a request for service on the Nintendo website. They sent me the shipping materials and exchanged my Wii for a new one. With all my data copied over too! You may be without it for a few weeks, but its worth doing now. You don't want it to get worse and be out of warranty.