Saab: noise from auto climate, ventilation fan, precise conditions

Question
It makes a clunking sound only when the auto climate is on. The noise will stop when I turn on the economy part of the system or when the car is moving.  I had the fan replaced but it still makes the noise.

Answer
My hands on expertise is limited to pre-1991 non turbo 900's. "Auto climate" sounds like it is from a newer model so I can only answer generally. Also. I would need a better description of the precise conditions under which the noise occurs, as well as the perceived location of the noise source.
But since all a/c systems consist of three moving parts (the a/c clutch, the a/c compressor, and the ventilation fan,) I would check those in that order.