Destrey Shamen

This is a problem I've had before, I found the solution once and now I forget how to fix it. With some mesh items, when I scroll out or walk away from them they turn into triangles. But when I get closer to them, they go back to normal. It's kind of like when you first loading in and every thing is loading, that's what it's kind of like. It's driving me crazy because I don't know how to fix it! :(