Hi Zebra123, and welcome to cruise-chat;
I think I can put your mind at ease here; I've been on the Diamond Princess and her sister, Sapphire Princess and, while I was not on Aloha deck, I never once heard anybody complain about noise on Aloha deck from above; and people are usually pretty vocal about things like that. The only things that can cause problems are jogging tracks, shuffleboard courts and basketball courts--none of which are above Aloha.
And I've never read a post here complaining of noise from above.
As for motion, Diamond Princess rides like a "Cadillac on an interstate", to borrow an expression from our beloved guru, Dave Beers. The bridge will make an announcement if they are expecting rough water so you can take your antidote of choice way in advance.
Aloha deck aft is actually a great location because of its proximity to the Horizon Court buffet, the Calypso Reef and Pool, and my favorite place on the ship, the Terrace Pool at the very back of Aloha deck.
Have a wonderful trip and keep in touch.