Its not noisy but not worth it at all. For the price you'll probably pay you could get a cabin with a balcony or window. Those cabins in the atritum kind of stink because you can see directly into the person's cabin across the hall from you as well as them looking at you. Most people just keep their shades shut the entire time.
We were in an Atrium cabin on the Explorer and loved it! It's great to be able to sit in the bay window and people-watch below. There is no noise, and it's fun to view the parades at night without having to fight the crowds. Four of us went and had two Atrium cabins, but on different floors. It was nice to be able to look up and see whether either party was in their rooms. I don't think you'll be disappointed if you book one of these cabins. We'd do it again!