No, it's definitely not that. I'm pretty sure that, whatever it is, it isn't exactly a "problem." It's just noticeable occasionally. Hmm, let me see if I can explain:

The best ways I can think of to describe this is to think of corduroy. It also reminds me of the surface of a screen for an old rear projection TV, the kind that if you run your fingernail down you'll get a sort of "zipper" sound.

Didn't I say I was horrible at describing things? I'm almost embarrassed to read that description, but it's the best way I can think of to explain it. If I get five minutes at the Wii this evening I'll try to capture an image of it.