I've installed the game on my hard drive when the game came out, but I always got suspicious that it wasn't reading from the hard drive, since my Xbox would still be loud after playing. I installed again, same issue. Today, it told me the disc was unreadable, and went to the dashboard, but it's installed to the hard drive. Anyone else having this issue?
Like you, I also have the game installed to my HDD. I have noticed times where it sounded like the disc was spinning in the tray well after the game had launched. Not sure if this is intended or a bug.