OK, under those nice fairings are, based on my count of intakes, three engines.
Was also going to say nay to this, more than likely cooling for all that input to the mgb.
Seems like resonance between the wings/nacelles and the wide tailfins.
There was severe resonance in exactly these areas and I dare say that the chaps from EC may even have been a little surprised.
Cattletruck did elude to it in his comment:
I would think the lower moment of the pusher/puller props from the MR head would contribute significant pitching movements (like a boat) as the couples fight each other for equilibrium.
This a/c must surely be a testbed and I am sure that if it goes into production will look nothing like it does now. Someone mentioned shrouded rotors - anyone remember Dowty?
Dowty's Ducted Fan Islander
Not only do the props need to become ducted fans or similar but I am sure the entire wing assembly will be modified to accommodate optimal dynamic relation with the main and side rotors.
If they didn't go for fans then the side rotors should ideally become rearward facing (if the cg can be maintained) to encourage better safety.
Just taking a wild stab at the vibration from the side props .. my guess is that the pylons are too flexible and probably have little by way of damping measures.
It will be interesting to see how x-cubed ends up!
Earl