Posted for "Charles R. Patton" <charles.r.patton@ieee.org>:

Scott,
Thinking back on my aeileron counterweight resonance with the engine speed, is it possible that the resonance is due to elevator push-pull tube tension?  Your comment about engine speed seems the most telling to me.  During climb, the tension on the push-pull tube is different than in level flight.  It is easy to imagine that going in and out of resonance.  A simple test would be to take a bungee cord and pull at right angles on the tube at mid-span and see if the characteristics of the hum change.

Charles Patton
360JM