Why is there a noise when the sound barrier breaks?

You might have noticed on your front page the question regarding the first human invention to break the sound barrier. I won't give away the answer, but it does puzzle me as to why there is a sonic boom when the sound barrier breaks. Is it a phenomena or can it be explained scientifically, or better yet in layman's terms? Is this the same occurrence when we snap our fingers? I've tried to make the same 'click' sound by flicking the fleshy part of my lower palm with a finger on my opposing hand, but with barely audible results. So I ume it is a mini-boom going on from finger snapping. Am I right?