I’ve had my 2016 SD V8 L405 about six weeks. It’s fine 54000 miles. Driving to Somerset and back (about 100 miles each way) I’ve noticed a slight drone at 50 mph+. This is only under load and disappears when decelerating. It’s very quiet and only just noticed it. The tyres are recently balanced and everything else is in order. It does this in straight line and doesn’t vary on left/right curves in the road. The car is running Pirelli scorpions on 20 inch rims if that helps. Could this be something simple or common? (Hope nothing serious 🤞) "There is no replacement for displacement" - W O Bentley

Likely a diff starting to become noisy. might stay like that for years. Had very similar on my Sprinter. Started with a very slight drone under power (could hear something in the background) but quiet when power was removed. It got real noisy in around 600 miles to the point I limped home, even then, quiet with no load but crazy loud when I touched the throttle.

Start with changing the diff oils. Pretty cheap and doable DIY for little money. You might catch it before it gets worse SDV8

check exterior trims - could be A pillar or front scuttle? or heat shield under car?

What are the revs at this point? Mine does it at circa 1300/1500 revs (under load only) and is the exhaust heat shield  2013 L405 Autobiography Baltic Blue
2007 L322 Vogue Buckingham Blue

Used to get this all the time , until her indoors stopped talking

Here all week , get your bookings in.