Probably the lowest deck ( Riviera deck, although I've heard this noise on Main deck as well) way, way in the bow,,,where you'll hear lots of noise from the waves hitting the hull of the ship all night when underway, and mechanical noise from under you all night, and the LOUD noise of the anchor chain when you arrive very early in the morning at a tendered port,,,,or,,,,within 3 or 4 cabins from the stern on the same deck, where you'll hear the constant rumble of the engines, and props when underway. I've experienced both, and the bow is no doubt the worst. You'll finally get used to the droan of the engines and props in the stern, but the noise in the bow changes constantly, so you will never get accustomed to that noise.
If you are a light sleeper, you do not want to be in the very back or very front of the Riviera/Main decks. Early in the morning you hear the anchor/engine and late at night you can fill the vibration of the engines and the gears shifting.
If you are a late sleeper/early to bed person you do not want to be under the Casino, Lido Deck, Buffet, Dining Room. You want to be on a deck that is sandwiched between two other decks (Empress).
I live in NYC, go to bed very late and wake up very early so these noises do not bother me.
My worst cabin was a inside cabin (Riviera midship) on the Glory. These cabins are smaller than on other ships in that the beds can only be side by side rather than the "L" shape that give more floor space. I found the side by side configuration left very little floor space to move around. I perfer a Cat 1A with one twin bed or the standard "L" shaped inside/outside cabins.
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)