Completely random thought, feel free to disregard...

Is it worth placing a red laser in front of the tube and verifying the complete optical path (bit of smoke, video camera) to make sure the axis drives aren't causing vibration in the various path mirrors etc. What I'm thinking is position Y at min/max extremes and rapid transits across X, observing any oscillation in the optical path. Might be worth if only to disregard this effect.