Fun, indeed.
If you really want to investigate this, and if you can scrounge the gear somehow, it might be worthwhile getting your hands on the best microphone you can, at least so far as low-frequency response goes. The lower the better, since the phenomenon may actually be subsonic. (And you really need to take almost all specs on mikes with a huuuge grain of salt; many are wildly exaggerated.) Then try to capture a recording of it; a minute or two would probably be enough.
Then you could try to analyze it at your leisure, maybe trying analog techniques first (get a 'scope and look at it).