With the "cotton" due misunderstanding caused by improper knowledge of the term "sound barrier". This "cotton" true name "sonic boom." Plane, travel at supersonic speed, making the surrounding air shock waves racing air pressure. Simplistically, these waves can provide for themselves in the form of transmitting the flight of a cone with the top, as if attached to the fuselage nose, and forming against the movement of the plane and propagate far enough, for example to the ground.
When the boundary of an imaginary cone, indicating the front of the main sound waves, is seeking a person's ear, the sharp jump in pressure is perceived by ear as cotton. Noise impact, as tethered accompanies the entire flight of the aircraft, provided that plane moves pretty fast, even with a constant speed. Slam it seems the passage of the main wave sonic boom over a fixed point on the surface of land where, for example, is listener.
In other words, if supersonic plane with the same, but the supersonic speed began to fly over the listener back and forth, then heard a clap each time, after a certain time after the clearance plane over the listener on a fairly short distance.