I think you need to give that cabin to me and get another one. <VBG>
You have an excellent cabin! The stern balcony cabin has a wonderful stern view and a balcony that is about four times larger (deeper) than the other Cat D cabin balconies. These cabins are IMO some of the best on the ship. I had one on Serenade of the Seas (Sister Ship) and loved it. I think you will too. I had no problem with motion, noise or vibration, so I don't think you will have to worry about that.
Enjoy yourself, the cabin and the cruise.
Mike (Who loves stern balcony cabins)