I've never rented an apartment with central A/C, so I can't help much with that. I know with my window A/C unit, I have to set it for much cooler than I want in order to keep the humidity down.

With the noise, for future apartments, try and bring a friend along when you view the place. Have the friend go into another room and talk or play an iPod loudly, so you can get a feel for how sound carries from room to room. (It's possible that there'd be more sound-proofing between apartments than there is between rooms in the same apartment, but I haven't found that to be the case very often). Also, while you are in the building, listen carefully for noise from the units upstairs or downstairs, and noise from the hallway that might carry through the walls. If possible, try to see the apartment on a weekend or in the evening when the residents might be home, instead of the middle of a weekday when many people will be at work.

Seeing the apartment at the weekend or in the evening will also give you a better clue as to who else lives there--lots of young people, lots of older people, lots of kids, for example--which can let you see if you will fit in well with the existing residents or not.