The stadium doesn’t MAKE noise, it KEEPS the noise the fans make. And remember both teams have to deal with the noise.
It amplifies the noise the fans make and artificially increases the level over what the noise would be in a “ normal “ stadium. And it’s an advantage to the home team because the fans are not morons and quiet down when the Seahawks are on offense and increase their noise when the other team is on offense. You don’t watch football much do you?
The fans don't make the same amount of noise when Russell Wilson is calling out the cadence as they do when the opposing QB is.