I was cleaning the dust off my iPhone screen today, I have a black 3GS, and I noticed that there was a mark that wasn't coming off... I instantly freaked out (lol), and wiped it with a tiny drop of water and it still didn't come off. I can't feel the mark as a scratch on top of the screen, and I think it might be underneath. I have never dropped my phone and I baby it like it's a newborn. Any ideas?