Are you looking back using the rear view at the time at all? There was a bug where the game would freeze when you look back. I'm not sure of the details as it was supposedly fixed before I knew anything about it. However, I did experience a freeze on a couple of occasions, after it was supposed to have been fixed, where I looked back at the end of the race as a quake was simultaneously approaching. That's the only thing I can think of right now though, which may not be of any use. People here have experienced all kinds of bugs and freezes along the way since the game's release, so hopefully you will get some more suggestions.