The pattering noise is caused by the actuators/servomotors driving the Airmix doors in the Aircon unit. AUDI pride themselves on their aircon units making 'no noise'. Next to the Blower Motor, the servomotors are the next biggest problem for them in this respect.
The fact is that some are much noisy than others, so if you are frustrated with it, you should complain to your dealer to get them replaced.
Steve - you might have a point there. Her car (Honda CRV) is rather like a biscuit tine
Actually, she is so fed up with my complaints about the mess when I get in her car, that when I got home today it was totally clean - inside anyway; I do the outside!
Kaine - the pattering noise is not annoying me, I just wondered what it was.
Actually, I was hoping all the noises were really a secret turbo, so that I could get the power chipped up!
To be honest, these type of noises are always quite acceptable to the masses, however AUDI Engineering/QA are quite severe. As an engineer, sometimes I like to hear parts actually operating. Gives you the feeling that parts are functioning correctly.