I went to the 2007 game against the Rams. Had an extremely tight schedule, drove 10 hours through the night and watched the games, only to drive 10 hours home.
The loudest point in the game was after Romo made that crazy scramble. That's not to say that they didn't get loud at other times but the entire building was pretty wild after that play.
There were times where it seemed like there was one large mumble across the entire stadium as though people were just carrying on a conversation. IMO, it just didn't seem like the crowd was all that into it other than the big plays on both sides of the ball. Then again, I'm comparing to personal experience and I've been to a number of games at Allen Fieldhouse and that place gets out of control.