This is an experiment I conducted about 6 years ago after hearing some comments about a 'pop' heard during a rocket flight. Some believe that this is the sound of the rocket breaking Mach. It's actually the sound of pieces of propellant being ejected out the nozzle. You can't hear the sound of the rocket breaking Mach from the ground. However, it does make a sound, and I captured it. Please see the video and I would appreciate your comments on this. And, I would like to see someone do something similar!