Since I started my second play through I haven't noticed this yet. I am curious though, how many people are on 360 with this happening. And what version of the console do you have? That is always something to consider.
I have a white Xbox 360 Arcade with Jasper chipset from October of 2009 with a 20GB HDD and a 16GB usb that I use to install the game. Btw, what does the model of the system have to do with anything? All models should play the game the same. I have read an article somewhere on the internet about older Xbox 360s having problems with the game. Don't know if that has anything to do with it.