follow link on how to clear system cache....
http://support.xbox.com/en-us/pages/xbox-360/troubleshoot/hardware/clear-system-cache.aspx
Hope this helps some of you.
PS- I remember someone had commented on the possible cause of the grain glitch being due to continuing a saved game in single-player. That got me thinking. I wonder if you started a single-player game before the March 31st patch, then continue with the same game after the patch has been applied is the cause. I've seen people posting that if they prevent the game from patching, the bug doesn't rear its ugly head either.
I bought this game and start playing on Monday 04 April and i experienced the glitch.
The 3mb patch from 31 march wasn't just to prevent cheating in multiplayer ?