Renault Master humming and whining at higher speed - wheel bearing or gearbox?

A steady hum that increases with road speed is a classic sign of a worn wheel bearing. A useful clue that separates it from gearbox noise is that the sound changes intensity when you gently steer left and right, because the load moves from one wheel to the other. If ignored, the bearing develops play, which can overheat the hub and, in extreme cases, seize. The bearing is replaced as a complete unit.

How to tell a wheel bearing from gearbox whine?

Gearbox whine depends on the selected gear and disappears when the clutch is pressed. Wheel bearing hum is linked only to vehicle speed and reacts to steering. If the noise remains while coasting in neutral, the source is the bearing, not the transmission.