With the recent hot weather, if the rear of the car is in full sun for any length of time, the alarm triggers, the doors unlock and the back window drops as if opening the door. The central locking sounds a fault beep on the horn. The back window will go right down from the interior switch but not up. Sometimes the fault will clear by opening and closing the rear door. As soon as the temperature drops or if the car is moved to shade the rear, everything returns to normal. Any ideas?