Is it not the cabin trim? During climb and descent on the A320 you'll often hear clicking and banging as the cabin walls, bins, joins and doors etc make a bit of a racket! Its particularly apparant at the front and back of the cabin close to the doors. The doors make a slight clicking noise too. I've never been on one but perhaps it could cause the noises.
The pilots will probably not be aware as its noisier in the fight deck and they will probably have their head sets on too during the climb.