http://www.ign.com/articles/2013/08/08/ive-seen-a-real-xbox-one-kinect-game-in-action-andAnd believe the hype: the new Xbox is almost inaudibly quiet when running.
It's not much and it was mentioned mostly as a sidenote.
I believe all games will be required to install to HDD, so you can't play from a disc anymore? That alone will make the noise levels much lower, as it's often the disc drive that makes half of the noise