Aux heater fan under car switching randomly and draining engine battery

[Lez99]

2008 California 2.5L Diesel. Seems like what is the aux fan for the cabin heater has been switching on randomly and when if unnoticed,. drains the engine battery. This is not the cabin fan, there is no air coming out of the pillar, rather some sort of a safety fan that seems to be running of the engine 12V battery. Is this even possible ?. It certainly isn't the engine bay fan. Last I've noticed it has come on, when I unlocked the doors and stayed on all night draining the engine battery almost completely. Sometimes, after starting the engine and driving for a bit, the fan stops and doesn't turn on again. Sometimes is just turns on randomly in the middle of the night. I'm not able to attach a video unfortunately