I can't be sure but it sounds like the radiator fan, in many cars this can come on even when the engine is not running.
under you're bonnet in the engine
under the bonnet of my car/pickup,is a 7.3 lr powerstroke diesel engine,
subaru legacy engine is switched off when stop after drive
To protect the engine form the weather !
hood (or bonnet in UK)
Under the bonnet, in the engine bay.
The bonnet is conveniently placed at the front of the vehicle, directly above the engine compartment.
"Bonnet" is the Britsh equivalent of the "hood" of a car. answer the metal sheet covering the entire engine is Bonnet which is also sometimes called as Hood.
In the engine under the bonnet
Engine.
open bonnet
When you open the bonnet, it is located at the left front area of the car. It is just beneath the air intake duct for the engine, beside the oil dipstick.