Okay, I am feeling very dumb.
For me, the solution was simple. I couldn't understand why a program would be making noise when I had none of my programs running (as far as I could tell).
Solution: I downloaded several widgets the other day and didn't go through them all. There is one from "TheDashboard: Widget and Gadget Development"
http://thedashboard-widgets.blogspot.com/ for an aquarium. For some reason, the audio turned itself on today without me entering dashboard. So I brought up dashboard (F12 for me) and promptly turned it off.
So, I feel pretty dumb for now, but hopefully this will help others in the future.
Happy New Year!