Wow, I now have a project to work on when I unpack my studio.
If nobody else comes up with an answer I'll post one in a week.
I have a few old tube tone(sine) generators. They are really archaic, but for analogue devices they are relatively accurate. There was this odd transient tone in one of our booths. For some reason I sat there running a signal through the system until I heard the beats. A coworker of mine walked in and saw the smile on my face. "You really need to change jobs." He then grabbed the headphones and made the same face. Just a stupid story- but it was at least related to the topic.