hi,
i am investigating what and when goes to sleep on ignition off pr close of the car. I am fighting with battery draining and it is hard to get clue what actually does that.
during this investigation i noticed as below:

when i was sitting inside the car with ignition on - (car not started) - i was hearing smth like heart beat somewhere from the hvac area.

what is this?

also i was hearing a strange quiet stable hum from the rear.

what is this?

stopped after a while from the moment of ignition off - the same heartbeat stopped after ignition off.