Not so sure that Hitchcock ever made anything that qualified as Noir. I agree with the posters above that mention that with Noir there is a seediness, down on their luck aura that sort of dictates the scenes. Hitchcock's dark environs are almost always middle to upper-class scenes, that hint at a darker reality than can be covered by the glamor. Even choosing national monuments in North by Northwest, which by all accounts are held up as great treasures to be proud of, he chooses them as sites for potential murder.
To me, Noir lets you know what you're going to get right off the bat, whi