This was our second Carnival cruise and we loved every minute of it. With one minor/major (depending on the time of day) exception: cabin location. AVOID cabin #1006 AT ALL COSTS! It's right below the fitness center. We initially thought there was a cow or elephant stuck in our ceiling doing jumping jacks. Turns out it was just people running on the treadmill. Unless you like the sound of wildebeest pummeling your head at 6:00 am, pick another cabin. Luckily, it was not constant and oddly after the first day, we got used to it (thank you, Stockholm Syndrome). Also, kudos Carnival. They did extend a small credit on our account towards the 'premium' we paid for that class of balcony cabin. Apparently you have to pay a PREMIUM to have people burn off the previous night's trips to the buffet... on your head. The guest services guy said it was a known issue and there was nothing they can do and, anyway, not everybody complained. Which is why I assume they still charge a premium on the room.
Other than that, we had a great trip and a funny story to tell friends. I would suggest Carnival just sound-proof their treadmills or, you know, remove them. It's a cruise, for crying out loud. Treadmills should not be the priority.