In reply to Mr/Mrs gilliland we went on the Costa Serena last month ...this is a relatively new ship and huge (3,500 passengers) and the vibrations at the rear of the ship were dreadful when the thrusters were being used so it's not size or age that determines the problem!
We were forward of Midships on Celebration last October and it was fine..tho' we did notice the vibrations when we went to the theatre....have been near the back of Emerald and that was fine. Perhaps the secret is to go forward if you can!
I sailed on celebration last year, NEVER AGAIN! I suggest you try a larger ,more recently built vessel / different cruise line.It`s worth the extra money. Enjoy your cruise anyway.