Hi Max,
Thanks for your prompt reply, it's really appreciated
It's mounted on four ~12mm M3 hexagonal nylons standoffs, but it's also firmly encased in a plastic box:
I agree about the chicken and egg / motor and vibe problem! I think I will try spinning up each motor and prop in turn, keeping only one prop fitted at a time to see if any are particularly poorly balanced ... The motors, props, motor arms, chassis and AQ are all mechanically hard-mounted to each other, so there's nowhere for the vibes to go unfortunately ...
Do you think my AQ mounting arrangement isn't so good?
Many thanks David