Thanks, phys-l'ers, for your quick and thoughtful replies about the
ringing and beating rod.
To clear up a couple of fine points: the rod was not suspended,
pendulum-like, at the bottom end of vertical strings. Rather, the
(reasonably taut) strings came in from the sides and looped once
around the rod, like this (in crude dos drawing):
The swinging/bouncing was negligible and the rotation non-existent
after the rod was struck. I struck the rod from the side near one
end; I don't remember if I tried hitting it at other points. I
checked the ends of the rod to see if I could tell whether or not the
solidity of the rod was being faked. It sure looked solid under close
examination, but the makers may be cleverer fakers than I am an
observer. The cross-section appeared to be quite circular, but I was
not in a position to make any careful measurements.
Thanks, George, for the idea of producing the beats (on purpose) by
making a pendulum out of the singing rod. I hope you don't mind if I
plagiarize it for my classes here?... I think maybe I should try to
replicate the conditions under which the observation occurred and see
what the critical factor(s?) is (string placement, rod geometry, ...)
in the production and/or quenching of the beats.