When we took our Fantasy B2B, all the nights that the ship was doing 20+ knots there was the bad vibration. Yes, I liken it to those cheap motel vibrating beds. You couldn't sit on the bed (head against the headboard) to watch TV or read it was so bad. And in Animator's Palate it was so bad that there were several water glasses that "danced" right off the tables.
It was more than just the last night. There were several nights on the Eastern cruise and at least 2 nights on the Western itinerary that the vibrations were extremely evident.