Unfortunately, there is no good way to isolate this problem. It takes a good ear and a willingness to take the shotgun approach to repair. If you jack the car up, the load pattern on the bearing is changed. Any spall in the load area now doesn't see any load. So that doesn't work.
If you will be repacking the bearings, there are a few rules to follow:
All old grease MUST be washed out of the bearing. Bearing must be dried.
The bearing must be thoroughly examined. If it is less than perfect it must be replaced. Bearings are replaced in sets (inner race, outer race, & rollers). There are two sets per front wheel.
Setting the preload (bearing play) is critical. It must be done right! A dial gauge is the preferred method. But you can get by setting it by hand. To set the preload, tighten the nut snug (~40 ft-lbs) while rotating the bearing by hand. This'll squeeze the excessive grease from the contact surfaces and seat the bearing assembly. Back nut off nut until loose. Then tighten finger tight. Lock the nut. Preload should be good.
Bearings cannot be nicked, scratched, or corroded or the bearing is ruined. Even excessive polish is bad. Anything less than the original hone finish and the bearing is unfit for further use. Bearings cannot be hammered in such a way that the force is transmitted across the rolling contact surfaces.
You should get yourself a manual to learn how the repack a bearing with grease and how to exchange races from the hub.
95 E320 Cabriolet, 131K