We had Dolphin 734 on the aft. We loved the room our Balcony was almost 120 square feet. This was just a regular room not a suite. We had a Table and chairs and 2 lounge chairs and still had room to walk arround.
The noise of the water being displaced by the the propellers is little bit louder than a balcony on the side but we loved the noise it made. As for Privacy it was great!!!!!!
Engine noise and Vibration was almost non-existant.
All of the Princess Grand Class ships have suites in the back. If it was noisy, they would not have put them there. There will be a little vibration but there is in a automobile, too. It will rock you to sleep. I love it! You will love the Grand. I sailed trans Atlantic last May on her and it was awesome! Have fun and don't eat too much...