Xbox Humming, and cant read discs?

I put Halo: Reach in, havent played it in awhile, but its still relatively new, but the xbox began humming loudly, and it said it was an unreadable disc, i tried once more, same thing, then i put in LA Noire, ran just fine, still a little of the humming, then, it says disc is unreadable, this is an xbox slim, 4 gig, has not been overplayed, bought at gamestop, they said its never been played, refurbrished, what is going on? it was all just fine, playing some black ops, was it because i didnt go to the dashboard, then eject the disc?