Unreadable disc usually means some service time for your X-Box. Did you install it? That limits the amount of disc usage for game play. Starting over isn't that bad though, you already know some of your mistakes and can level up pretty quick second time
Yeah, it happens, if you can get it to install all the Xbox is gonna do is check the disc, to make sure you own it, and never reads the disc again, unless a cutscene or something, but my DVD never hums after I install a game, hope it helps. Good Luck.