That should be pretty clear just based on location of the sound. The evap leak test you'll hear from the rear of the vehicle in about the same place you hear the charging fan from when plugged in (if an Energi model).
If it is anything up front in the engine compartment, it isn't that. From the engine compartment, the list of parts that could make noise without the vehicle running are the vacuum pump for the brakes, ICE water pump, aux water pump for EV heating use (this is another Energi only thing), the aux transmission fluid pump (Energi only), and the cooling pump for the hybrid inverter.
For the items in the engine compartment, here's the rough locations:
ICE Water pump and aux water pump: Passenger side
Vacuum pump, aux transmission fluid pump, and hybrid inverter cooling pump: Driver side.
It has been noted previously, though I don't have any threads to link to atm, that it isn't terribly uncommon (and not common either) for water to ingress in some of the harnesses and short some of the connectors causing things to run continuously even at key-off. I think the most common part to experience this is the ICE water pump if memory serves.