This has just started, its a fairly quiet but noticeable whining sound that comes from the passenger side of the dash when I turn the fans on.

When turned from off to the first notch so you cant really hear the fans themselves, you can hear this whining sound.

Weirdly, when I turn the car off, you can still hear it both inside and outside for a few mins.

Any ideas?

The ECU has a cooling fan and that is on the passenger side of the car against the firewall in the engine bay.

Alternatively, it could be the FBH running - it comes on in low temperatures to speed up the heating of the coolant to help with emissions and also allow earlier heating of the cabin air. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Hmm it might be the latter then.

To give more info as I've found it....

The sounds stops when I turn the climate settings off, so no cabin heating or fans on, the sounds stops dead. Turn the climate back on and it starts again.

This sound is prominent for an entire journey of over an hour.

The sound continues to be heard from the outside for about 5 mins, after the car has been turned off.

I suppose you could pull the FBH's fuse so it won't run and see if the noise persists. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

What does FBH mean?

Fuel Burning Heater - I think. Barrie.
2005 RRS 2.7TDV6 from 2017 -2024. Best car I ever had.
Current: 2018 Ford Ranger Wildtrak 3.2

Thanks

Sorry, yes, it's the auxiliary heater that runs on fuel to help heat the coolant in cooler weather conditions. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Yep, it must be the FBH then guys.

Today the outside temp was 9c and the sound never started up at all

Good stuff - thanks for the feedback as it helps the next one.  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed