I have 2016 Renault Master. It starts whining/bearing kind of noise around 60kmh, gets much lower after 70-75kmh. It also gets lower on neutral or when clutch engaged but doesn't completely stop, can be still heard.

It got gearbox bearings replaced ~10k km ago. The sound is similar like before the gearbox repair.

I went to 3 repair shops, one said gearbox, the other two said its not gearbox or wheel bearings, might be the tires because there is no sound on lower speeds.

When you spin the wheels when car is lifted, there is no bearing noise from any wheel.

How can I pinpoint the problem and make sure its gearbox? Or any other ideas? It is a campervan and we travel to weird places, I don't want to have breakdown in a weird country middle of nowhere so I want to get it fixed somehow.