I bought my Macbook about 3 weeks ago, and while I was in the store picked up a Level 8 carrying case for it. I have noticed twice now that when I take it out of the case, there is a black tinted stain on the lid. A magic eraser takes it off with a little bit of scrubbing, but this can't be normal. Is this a flawed case or is it just a flaw with the white MacBook? Any ideas?