Most people say it’s Arrowhead Stadium in KC, which has reached decibel levels in excess of 116 dB, which is an absolute record for any indoor or outdoor stadium. That’s louder than the engine of a 747.
Seattle and Minnesota also regularly register over 100 dB.
What makes Arrowhead unique is that it is designed to amplify and preserve sound.
There was a 1991 game between the Bills without rules and the Chiefs. After one series, the Bills had to huddle because guards and offensive linemen on the Bills’ offensive line couldn’t hear quarterback Jim Kelly play line … at all.