Cold temperature, won't go into drive

My 2001 Forester just started having weird problems. When the outside temp drops below 40, it takes forever to get the auto shift to go from park to drive. The button on the side of the shifter will not press in, and my foot is firmly on the brake. I hear a clicking sound coming from (the dashboard? steering wheel?). After several attempts and perhaps after the car engine warms something? the car finally gets into gear. What is this??? Mechanical or Electrical?