A bearing in the differential could be noisy too, but a noisy wheel bearing is much more likely and common. You might be able to run the vehicle in gear on a hoist and listen with a stethoscope, but that doesn't put the bearings under load, and it can be real hard to identify the noisy part. A good bearing and a noisy one will often sound almost the same when not under load.
You can also jack up the rear wheels, then spin one wheel at a time by hand and feel for a vibration in the coil spring. Noise from the differential shouldn't transfer to the spring but you will usually feel a vibration from a noisy wheel bearing.
Be aware too that bearings don't typically cause a rumbling noise. They most often are described as sounding like the buzz of an airplane engine that changes pitch with changes in vehicle speed. The Chassis Ear is the fastest way to locate the source of the noise.
Pinion bearings in the front of the differential can cause a rumbling noise too but those can usually be identified just by standing next to it while it's running on a hoist. Those do not make the same buzzing noise as a wheel bearing.
Tuesday, March 10th, 2015 AT 3:49 PM