Just recently (sort of, up to a month ago) after not playing our Xbox for about a week or 2, our (my brother and I) Xbox 360 has started making weird noises while trying to read disc.
It didn't do this for a while, but it all of a sudden started. It sounds like it is scratching the disc, but they come out fine. It slows the game down a little, and is starting to getting annoying. Now, for one of the disc, it says under the dashboard "unplayable disc".
Gears of War
And maybe more.