There is a technical service bulletin that may be related, here is the number and a brief description of the symptom: TSB 01-12-06
FORD: 2002 EXPLORER
Some vehicles equipped with the manual A/C system may exhibit a continuous clicking noise from the blend door actuator when the blower speed is set at the #2 position and the temperature control knob is set between the 12:00 and 2:00 position. This may be caused by separate power sources to the blower motor & blend door actuator
counteracting each other resulting in a clicking or fluttering noise.