We just returned from a 5-night stay at the Contemporary (April 2003), and 3 of those nights were in the Tower. We were on the 10th floor, on the side above where the shops are (Chef Mickey's is on the other side of the large 4th floor "lobby"), on the Magic Kingdom side. We NEVER heard any noise that bothered us -- so, I think it may depend on how high up you are AND if you are on the side right above the restaurant or not. We are very, very light sleepers -- on our first two nights, which were spent in the North Garden Wing, we got no sleep at all. The noise of people coming back to their rooms at all hours of the night prevented us from getting any sleep. (I do not know this to be a fact, but we guessed that the wings were added later, and that the construction quality of the wings is well below the quality of the Tower. The Tower was great -- no complaints. In the wing we also heard every footstep taken on the floor above us, and all the room noise from the rooms on either side of us AND across the hall.)
We plan to stay in the Tower again in the future, but will never stay in either one of the wings again.
Finally, if you are concerned about noise, mention it when you check in and I'm sure they will do their best for you. I'd recommend asking for a higher floor, on the shop side....