Hello all. I've read all the Haldex/rear diff threads and understand that it could be either but my problem seems a little different. It's a low level whine/hum sound when driving from cold, It never gets louder and after about 15 minutes disappears. I've had it for about 5 days now and it has not got worse. The car is April 2013 with 82000 miles. Any ideas gratefully accepted.

I have a very, very, faint whine when starting from cold. As it seems to increase pitch with engine revs, from nothing, I assumed it was turbo air noise.
It is a very light, non mechanical whine, and dies to nothing within the first mile or so. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

"I have a very, very, faint whine when starting from cold. As it seems to increase pitch with engine revs, from nothing, I assumed it was turbo air noise.
It is a very light, non mechanical whine, and dies to nothing within the first mile or so."

Thanks Ian. Would the turbo air noise not come from the engine compartment ? The noise I hear does sound mechanical and seems to come from under and to the rear but is different from the Haldex/diff problems reported by others in not getting worse over the time it's been happening and disappearing after about 15 minutes each time.

I don't know if you have climate control, but I have noticed sometimes from cold a hum that then fades away after driving a bit. Turns out it was just the air con fan adjusting interior temp to a pre-set temperature but sounded like it was coming from somewhere else. Noises can be weird.

thanks donk