[Bigdav160]

The pinion bearings are pressed on to the pinion. There is no way to "inspect" the bearing without removing the pinion. At that point you are at least reconditioning the axle.

Was the whine there before the seal replacement? Then likely you had a bearing problem combined with the leak. Pinion bearings spin fast and are lubed by splash lubrication. They starve for lube when the axle is run low.

If the whine started after seal replacement it's likely the pinion bearing preload is off. Those tapered bearings are not tolerant of too much preload (nut too tight) and too loose they let the pinion walk back and forth messing with the meshing of the ring gear and pinion.