The noise sounds central and mechanic had a look and says it’s either the rear diff or prop shaft bearing, only thing is the noise is loudest around 30-50 mph and is still audible when in neutral.
He said there are metal filings in the rear diff oil.
Any thoughts. Current: MY11 SD4 HSE / Sterling Quartz 2010 caravan

Previous: MY11 TD4 GS / Bailey Bordeaux 2002 caravan

If there is metal in the diff oil, then the diff input bearing is breaking down.
Get a reconditioned diff fitted ASAP, as mine seized solid at 45 MPH, resulting in the wheels locking and back end stepping out, leaving my stopped in the middle of the road. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Thanks Nodge I’ll get it sorted ASAP, also is it the done thing to get the prop shaft bearing changed at the same time? Current: MY11 SD4 HSE / Sterling Quartz 2010 caravan

Previous: MY11 TD4 GS / Bailey Bordeaux 2002 caravan

\IIRC You may have one or two prop shaft bearings depending on the age of the car.
Propshaft bearings don't get much a mention on here so I wouldn't change it/them unless there is an obvious wear. Jules