Periodically, the game will hang mid-level.
The problem happens during later missions (starting with Flatline), for no apparent reason.
It can also happen after the game has been paused for a period of time.
This is often preceded by stuttering music or loss of sound effects.
Then the game freezes, and a dirty/scratched disc error pops up.

I assure you, this happened when I bought the disc new, and on the FIRST INSERT of the disc.
There is no disc scratching or dirtying involved.

This happens on a friend's Xbox and disc, as well.
As far as I know, we both have version 1.0 Xboxes

I have contacted Microsoft's support hotline and followed their advice(deleting the game files and making sure the system clock is always set correctly), but the problem persists.