we have 2 identical X5 diesels, One does the fan /whining noise and the other one is pretty much like quiet exception of normal expected sounds.
I can understand the regular electronic based sounds, cooling down , shutting down some systems and etc.. (that may include the diesel DEF and all that.
I am talking about like a fan sound coming from passenger side engine compartment - around right under the rear edge of the engine cover towards to windshield (not the cooling fan in front of the radiator).
it starts after you shut off the engine and slowly disappears in about 3 or 4 minutes.
FYI, this is not the noise coming from the fuel pump before and after you start and stop the engine. Normally after you stop the engine, there is a consistent static noise which I think coming from the fuel line or something related to that and lasts about 30 -45 seconds. That is normal and not the issue i am addressing here.