Whistling/Humming sound from gearbox/axel

Hi all,

Thanks for allowing me to join this forum.

I own a 2016 Range rover sport (L494) HSE Dynamic. Recently, I have started to notice a whistling/humming sound coming from what seems to be either the gearbox or front differential. This humming noise comes right before my car switches gears, and I tend to notice it more when going downhill.

Any advice as to what this noise is?

Many thanks

If you hold the gears using 'S' is it reproducible at specific engine revs? what engine is fitted - is it the SDV6 or SDV8?