pop in audio

At the start of each clip recorded with an external microphone there is a pop. The pop is not recorded on the clip but occurs whenever the clip begins, no matter the in point. Clips recorded without an external mic do not pop at the beginning. Any way to eliminate the pop and to prevent it in the future? Using FCE HD, Canon EOS 1D Mark IV, Sennheiser ME66 microphone connected to the camera.

Thanks