With that described sound and it only occurring around 15C+ it sounds like it could be Turbo Flutter.
It has been discussed on here a few times and there are examples on YouTube to compare.

0:48 on

https://www.youtube.com/watch?v=Rr5Hl2r4Rq4

I don't get any front wheel spin/scrabble. Initially I thought I was getting rear wheel scrabble but now I am sure it's just noise from the rear which probably means something to do with Haldex, or perhaps Gearbox.Strange thing it is temperature related ?
Next I will pull the fuse on the Haldex to see if it goes away.. FL2 SD4 XS 2013 Orkney Grey

Telco wrote:

With that described sound and it only occurring around 15C+ it sounds like it could be Turbo Flutter.
It has been discussed on here a few times and there are examples on YouTube to compare.

0:48 on

https://www.youtube.com/watch?v=Rr5Hl2r4Rq4

Does the sound occur if you are stationary and plip the throttle?

If so read this,
https://www.freel2.com/forum/post434719.html#434719

To me it doesn't sound like transmission, more like air/intake leakage or malfunction.

Also, if working correctly, your FL2 (Haldex) will always pull away in AWD, before at about 20mph becoming FWD. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

Sound doesn't appear when stationary and blipping throttle.

If it isn't Haldex, it might be Auto box . Could it be slippage from inside the box? Yet it only occurs in warm conditions? FL2 SD4 XS 2013 Orkney Grey

My MY2011 FL2 used to suffer from Autobox 'Flaring' occasionally, but this only occurred on warm days, when the autobox was fully warmed up. It happened when the gears changed when drifting along on a light throttle.

Its a known fault as explained in this Volvo document.

https://www.ipdusa.com/Articles/678/Volvo-...-Flare-etc

t was in this thread.(to me, it felt like a slipping clutch)

https://www.freel2.com/forum/topic31892.html?highlight=flaring FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

Sounds like " flaring " describes my problem . It happens between first and second under moderate throttle on warm days particularly when the box is warmed up.
Not enough of a problem to consider an expensive rebuild so I'll look inside having a box flush but apprehensive that it might cause more issues than it solves?

Did you ever solve it or just live with it? FL2 SD4 XS 2013 Orkney Grey

Update

So I removed the Haldex fuse ( FB1 in the boot on MY13 facelift ) and drove for a few days.
Slipping noise stills occurs so at least I know it's not the Haldex.

Just to reiterate

A cha cha cha slipping noise from the rear of the car sometimes occurs when accelerating under light throttle under load. Sounds like rear tyres spinning but it's not. Only happens in warm conditions - plus 17 degrees or so.
Doesn't happen under heavy throttle.I

How can it still happen when the rear drive is disconnected? Could be Auto Box related but it sounds too far back.

Any ideas welcome? FL2 SD4 XS 2013 Orkney Grey

Sounds like you need some chassis ears. Microphones you strap to suspect components and record the output while you drive.