I would look at the "Lift Link"...and transmission mounts first....then consider the Collective Friction system. If the oscillation decreases with your hand off the Lever....it is probably a lack of friction on the collective.
The Maintenance Manual has a section on how to air test for pylon rock. It involves a stick stir while in climbing turns....the oscillation should dampen out after no more than 2-3 cycles. (Memory tells me anyway....)
What you are describing does not sound like Pylon Rock. Also interesting is it only occurs while slinging a load and not doing just internal load carrying.
That points to the lift link or a load rigging problem it would seem.
Last edited by SASless; 9th Nov 2012 at 12:28.