A. is it something stupid like the rear seat HVAC system working? I know mine is quite loud...

B. Check all the tyres for saw tooth type wear, this phenomenon happens often...

Do NOT try changing your rear prop bearing as it will never be right imho... Change the prop...

I’ve turned the HVAC off but it’s still there, excellent point on the tyres, I had an A6 that used to eat rear tyres that made a similar sound, they ‘looked fine’ to my untrained eye I’ll try swapping the tyres round see if the noise moves  1972 Series 3 full of character
1985 90 pick up went anywhere
1992 90 Exported
2007 L322 that was an experience
2010 D4 more versatile than a Swiss army knife, now gone
2011 L322 4.4 VSE

What tyres are on there at the moment? 2012 TDV8 Vogue (L322)

255/50/20 scorpion zeros, can only see one front date mark 22 the rears are both 19 1972 Series 3 full of character
1985 90 pick up went anywhere
1992 90 Exported
2007 L322 that was an experience
2010 D4 more versatile than a Swiss army knife, now gone
2011 L322 4.4 VSE

You can possibly rule tyre noise out unless they have any abnormal wear patterns. 2012 TDV8 Vogue (L322)

They look fine to my untrained eye, I’ll get the sons GoPro mounted underneath later see if it shows anything 1972 Series 3 full of character
1985 90 pick up went anywhere
1992 90 Exported
2007 L322 that was an experience
2010 D4 more versatile than a Swiss army knife, now gone
2011 L322 4.4 VSE

Chickened out on the GoPro couldn’t face the explanation if it went bouncing down the road

Had it over the pit today, the only thing I saw that could be related to possible wind noise was the heat shielding near the rear prop bearing looked like a bit was missing, also wondered if the transfer box should have a cover / tray below it?

Tyres all appear ok, some small cracking but nothing of concern

Think it may be case of it just makes that noise until something shows itself

Click image to enlarge