Here's a problem that's been bugging me. We know that we get sonic booms because of the Doppler effect since, for an example, the jetplane over takes the soundwaves that it emits some time ago because it is travels faster than the speed of sound. The overlapping of new sound waves it produce will cause the sonic boom. (Feel free to correct the physics, I'm new at this topic) Let us suppose that we are an insubstantial observer following behind the jetplane at exactly the same speed. What would we actually hear when the plane breaches the sound barrier?