One thing to note: I originally had the sound files cut so they started tight against the audio waveform. However, when I clicked a tube, I would get a double shot, like "bang ba". I then added a few frames a silence in front and behind the audio clips, then I got just "bang". I assume it is because when the loop resets, it plays a few frames again.\
And a request: I cannot get cycles materials to work, they always turn out pink. If someone could set up a cycles material with this blend file, either a black plastic tube with ridges, and/or wood planks, and/or the white tubing (which is supposed to be silver duct tubing), I would definitely study the file to learn.