Rear A/C unit clicking noise

My 03 Explorer with rear A/C started to click when it is on and the temperature is set on cold. Clicking goes away when temp is turned up. Clicking noise is in the left quarter panel of cargo area. I popped the small grate near the jack storage area and saw a large balck plastic box where the blower is mounted. The clicking is in that box. Clicking stops when the front overhead blower switch is in Off position. Will start clicking in all of the other positions and will stop when temp is turned up a bit. Noise sounds like a relay opening and closing. Any ideas? Vehicle is still under warranty but I want to know if anyone else had similar problem and solution so that I can pass the info, to the dealership. This may be a rare problem and I hate going back and forth if they have to "guess". So any help is much appreciated. Thanks in advance.

It was the control motor and blend door for the rear air conditioner unit. BTW if you hear the clicking noise, turn off the rear a/c ASAP, otherwise you'll have to replace both the motor and blend door. The problem was the blend door initially.