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Brendan,
Vibration in mounts and their optical systems are quite a real phenomena.
I was exposed to a significant vibration problem with a large telescope mounted on a P-ME.
In order to counterbalance the scope it was considered easier to make one large counterweight and add that to the end of the counterweight bar rather than many extra weights all the way along the bar where they served less effectively - which would have meant extra mass was needed and that was the purpose of the exercise - to keep the total mass contained.
The single large weight introduced a significant vibration (probably a resonance) into the system that was unable to be controlled even by AO.
The mounts motors are effectively being pulsed or frequency controlled and other components such as AO and fans introduce vibration into the system, if a component or arrangement of components end up in resonance then its very difficult to dampen the vibration in some cases - noticeably that one.
Wind gusting and Wind induced vortex shedding vibrations are also a cause of vibration in telescope systems.
Rally
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