So the fan/pump noises are a Tesla in "Standby"? As in no HVAC for the passenger cabin, but if the edutainment computer "gets warm" it'll cool it, and, um...does this mean the main Tesla battery is in use, or just the little 12/14V battery?
So I should be able to test this by excluding home, and once confirmed I could just un-exclude home? (I mean what if I leave the garage open by mistake? I need the Tesla to capture video of any dogs that come by, or anyone dropping off packages!)
The WiFi in my garage is pretty decent, it is almost just below my office where the house's WiFi originates. I haven't' checked to see what the Tesla specifically thinks of it, but it is "all the bars" on my phone so it ought to be at least close to full reception for the car. It definitely had no problem getting a software update via the house WiFi.
No, the low voltage battery does not have the capacity to run the Tesla low voltage systems. The low voltage battery only has the capacity to power the LTE modem, BT modem and the door locks when the Tesla Model Y is in Sleep mode. The low voltage battery is used to power up the Tesla vehicle's computers Once powered on, the Tesla vehicle powers all of the low voltage systems using the power conversion system (PCS) The PCS is a high voltage DC to low voltage DC converter.
When the Tesla Model Y enters Sleep mode, periodically, the Tesla Model Y will wake from Sleep mode and charge the low voltage battery using power from the high voltage battery using the PCS.
Also, the Tesla Model Y must be able to enter Sleep mode, occasionally, while parked so that the battery management system (BMS) can measure the open cell voltage of the cells in the high voltage battery. The OCV data enables the BMS to better estimate the state of the battery over a range of state of charge.
Just get a Ring security spotlight camera or similar to monitor the front of the garage. Leaving the Tesla Model Y in Standby mode (this includes whenever Sentry mode is active) wastes power, is inefficient as the Tesla Model Y consumes ~230W in Standby mode (only 25W when in Sleep mode.)
The sounds you hear coming from your Tesla Model Y could be the BMS cooling the battery by circulating coolant or the thermal management system capturing heat energy from the passenger cabin or infotainment computer. While uploading data to Tesla's servers or downloading an update the infotainment computer may need to be cooled.
Cell balancing can take place at the end of a charging session, automatically. This could cause the fan to run to cool the battery. Your Tesla Model Y is an active part of the Tesla fleet and can run Tesla directed routines while parked, at any time.