The propulsion problems we had on our cruise and the non-stop 24/7 vibrations - especially in the aft section of the ship - were definitely tied together. In the dining room while at sea, the water in our glasses on the table was in constant motion - mostly rippling on the surface. The vibration noise (resonnating) thoughout the dining room was annoying and a hinderence to conversation. Much like an multi-engined airliner when both engines are not in proper synch.
While I agree that thrusters do cause vibration during manuvering, this was a whole different issue.
I am a licensed captain - 100 ton coastal (better known in Coast Guard language as a 6-pak license) - and spent 25 years on boats and ships of all sizes for pleasure and work. I know vibration and I know propulsion issues. On our cruise, the 2 were tied together.