What would cause a whine down noise when shutting engine off?

A whine down noise when shutting off an engine could be caused by several factors, including a failing alternator or other electrical components that continue to spin after the engine stops. It might also originate from the Power Steering pump or a worn accessory belt. Additionally, air being released from the fuel system or vacuum lines can produce a whine-like sound. If the noise persists or is concerning, it's advisable to have the vehicle inspected by a mechanic.