My old car only had climatic and not climatronic, so was easier to diagnose in my case as it was manually controlled.
The yellow elbow joint on the control flap motor had come off, so it was stuck blowing cold air as the vent was shut.
I replaced it but noticed as the elbow moves, it can pull the whole mechanism together as it was only screwed at the top of the body, not the bottom too. I think this adds to jerkiness and clicking noise.
My ED30 does it as does our Altea, just poor design really.