humming sound on 1999 Infiniti G20

after car is turned off, there is a humming sound that contiues for 15 secs.

Asked by for the 1999 Infiniti G20
Is this humming sound from the engine compartment? If so it is probably the electric cooling fan on the radiator and this would be normal. If inside the car again I wonder if it could be related to the heating and air conditioning fan that is switching off but you hear it rotate while is switching off.
3 more answers
Fuel cap - pressure equalization. Normal.
There is a humming sound that continues constantly after it is shut off
If sound is from rear of car it could be the antenna retracting or attempting to retract