Noise from rear end at hwy speeds. on 1998 Dodge Ram 1500

I had a differential service done. Replaced front and rear brakes. Still the noise is there. Brake serviceman said I would have to take to a transmission place to find noise and repair. It is something in drivetrain.

Asked by for the 1998 Dodge Ram 1500
The front pinion bearing in the differental is very small and very common for failure. Fix it ASAP!