This is all I could find on noise (other than crowd noise -- that can be as loud as you want as long as you want):
"Persons subject to the rules including bands, shall not create any noise that prohibits a team from hearing its signals...."
But I noticed on Saturday that the bands and the piped in music often continued for several seconds (5-10 seconds at least) after the ball was whistled in, the clock was running, and the teams were already at the line of scrimmage.
Anyone know when the noise is supposed to stop? Was this technically a violation? What happens if the refs decide the noise is going too long?