Microsoft Halo 3 for Xbox 360 "disc plays noise screen" Questions

...plays all games except this one ok so back in febuary i bought a used halo 3.. i played it alot.. so august i took it out one day and it had a small crack in the middle ..but it still played.. but ...

...noise like the game disc was being scratched so i quickly put the 360 down and take the game out it didn't look like it was scratched so i then turn off my 360 and put it in its proper place I ...