curious to know what whirring sound is

[nu11eaf]

I often hear a whirring sound behind the dash a minute or so after turning the engine off and still sitting in the car, its sound like a small electric motor moving a flap or something, I know this is normal and I used to hear this in my MK 1 XC90's as well but I wonder what it is, does anyone know what the noise is and what it does.
I am only curious to find out what it is, not concerned as I know its normal.

[Chief inspector]

The heating and cooling is controlled by a number of air dampers directing the air over the cooling and heating coils to get the desired temperature, then another set to direct the air to the selected ducts.

These reset back to zero position at switch off ready for the next start and to seal the cabins air off.

[Philip Fisher]

Mine does that too. Getting a touch louder with age....

[Haldex]

I’m more curious to know what’s the whirring from under the hood AFTER I lock the car.

[crusted lark]

Originally Posted by Chief inspector

These reset back to zero position at switch off ready for the next start and to seal the cabins air off.

According to my old BMW manual the vanes go wide open so that you have ventilation in the event of a future system failure.

Originally Posted by Haldex

I’m more curious to know what’s the whirring from under the hood AFTER I lock the car.

The fan, I'd guess.

[Quacker]

It is an electric water pump that continues to cool the turbo and possibly the cylinder head after shutting down.

[nu11eaf]

No this is a behind the dash noise that only last less than a second as though something is being activated briefly, Chief Inspector may be correct with the climate flaps, its not a sound like a fan or pump running more a quick Bzzz.
It only happens after a delay If you sit in your car for a while after turning engine/ignition off, its not something that is continuing on after turning off.
Had this on my other XC90's as well.

[gaby]

Originally Posted by Quacker

It is an electric water pump that continues to cool the turbo and possibly the cylinder head after shutting down.

I assume your response is about the noise under the hood?
Is this a diesel-only feature?

[Dave©]

Steering wheel lock?

[nu11eaf]

Originally Posted by Haldex

I’m more curious to know what’s the whirring from under the hood AFTER I lock the car.

A few years ago I asked my service tech about a short bzzz under the bonnet after turning off and locking the car and if I remember correctly he said it was the electronic throttle body resetting or recalibrating which is normal on turning off.
This is a similar noise to the one behind the dash that I refer to above, and as Quacker says there can still be cooling fan or cooling pump running, not sure which noise you are hearing.