I found at least one old system that did this (although the version I heard related to the old mainframes Edinburgh University had decades ago):

EDSAC II had a speaker to help with debugging and this "feature" was also incorporated into versions of the LEO, the worlds first computer for business applications:

http://en.wikipedia.org/wiki/LEO_%28computer%29

I wonder if something similar could be created for the state machines in the article - giving each state it's own tone?