Ticking sound from the ventilation unit

Hi, have a E39 1997-model.
When I turn of the engine, I hear a ticking sound from somewhere under the radio or the ventilation unit. What is this sound? Will it drain my battery?

Nevermind, this seems to be the answer..

http://motorqa.com/question/1/ticking-sound-from-ventilation-on-bmw-520i-1997