I just got a brand new Clavinova CLP 645 and I couldn't help but notice from the first touch how noisy the keyboard is. It's not just the thud when the keys reach the bottom, but there is also a clicking/squeaking sound that goes with it which is incredibly annoying and distracting when playing. Did I get a defective copy?
Yes, it is likely that you have a defective unit. The wood keys are more for the "feel" of the play: the sensor strip that the keys hit are plastic and Mylar. It may be that something is misaligned in the key section. As Tim commented, check with the shop you purchased it from.
I think I can categorically state you have a defective unit, and should return it. Faulty keyboards are not uncommon.
As support for this answer, as well as personal experience I can cite two replies describing similar situations, and one that confirms your keyboard WAS faulty. All, however, were deleted as irrelevant.