I saw this trailer for the new movie Ironman, which comes out later this year.  I should probably add that I have nothing to do with the movie.

If you skip to 2:20 (the last 9 seconds), Downey goes supersonic, creating a shock wave which then dissipates as I assume he gains velocity beyond Mach 1.

Wouldn’t a second shock wave, known as a bow wave form at the base of his body?  Would we hear anything after the sonic boom? two booms?

Here’s a well-done page where I found some information. 

Addition:  Photos of an F-22 stealth jet going transonic, clouds forming;  Blue Angel bails out at supersonic speed and tells his story.  Space shuttle breaks sound barrier.   

Video here gives good overview.