That does sound weird. Do you happen to have any pictures of this by chance? Does the whole screen go black or is it just black stripes that appear when you move your character?
From my experience, when the whole screen goes black, it usually indicates that your lcd is about to die out on you, but it might not be the case here if it only happens when you move your character.
Does this happen with any other game you play?
In my own Animal Crossing game, when I have too many items scatered around town, sometimes when I move my character around certain areas, I see a few black stripes across the screen, but it goes away once I've cleaned up. I wouldn't know if this is your case though.