Including one game where Utah fans stormed the field and tore down a goalpost. I think it was one of those 34-31 games in the 90's.
On the other side of the coin, I will admit that the crowd last Saturday at the U was not particularly pumped up. The most agitated people got was when a couple of dillweeds were throwing snowballs onto the field, especially the time when one of them almost hit a Ute player.
I'd say maybe it's Utahns in general, but Jazz fans can make a lot of noise, and presumably those are the same people cheering for Utah and BYU.