It can be because of noise in the PWM outputs. If the camera draws power from the PWM outputs, I would recommend using an LC(coil-capacitor) filter before the camera. He had similar problems when the backup battery was low. Noise can temporarily lower the voltage, so i suspect this to be the cause.
Here's some info on the LC filters:
http://www.tpub.com/content/neets/14.../14179_204.htm