thanks for the tip kat. i have checked the armature modifier and envelopes are disabled. i've never actually used those as i don't really understand them, so i just work with vertex groups.
i think in this case blender was just getting confused as to the bones rotating within the mesh, because in my first attempts at rigging this, after 90 or 180 degrees rotations, parts of the mesh would snap into a weird deformation. but at least it's consistently working now i rearranged the deforming bones and added in more controllers.
and thanks very much for the compliment, one of the aims of these is to look alien/otherworldly.
re the more noisy videos, are you referring to one of the three i posted yesterday, or the older ones?
other than the highly reflective/metallic ones, most of my videos have a deforming psy cloud background, which often has a high frequency, intricate pattern mixed in with the clouds.