ah but Laura, there are other vibrations that aren't necessarily sounds... (Call me for more info, heh heh heh)

oops, me bad.

okay... sound:
   1. Vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing.
   2. Transmitted vibrations of any frequency.
   3. The sensation stimulated in the organs of hearing by such vibrations in the air or other medium.
   4. Such sensations considered as a group.

So, the primary definition refers to being capable of being detected.... so the sound is exists upon action, not the reaction. Or something like that.

Brian.