I've been to Soldier Field and the old Indianapolis Dome (before Lucas Oil field), and neither one was anywhere close to the Ralph in terms of noise. But then again, I went to a Bears-Packers game where the Bears got spanked, and the Bills-Colts game I went to was in the early 90s when the Colts crapped the bed. So no surprise it was not loud in either place.
Edit: the only other stadium I've watched the Bills at was in Madison for a Packers-Bills preseason game in the early 90s. It was an odd experience. The place was packed, and the fans were seriously into the game, even though it was a meaningless preseason game. When Kelly was hit going out of bounds and was shaken up, the place was roaring with approval, as though it made any difference. Those were some hard-core fans.