Is this the same vehicle where you suffered the axle nut problem? Did the axle slide out easily once you removed the nut?

The 124/129/201 rear bearings are a sealed unit pressed into the wheel carrier and onto the wheel hub, it is difficult to observe radial or lateral movement unless things are very worn. Movement early on will be axial, more inward and outward than up or down or side to side. With the rear end off the ground and the caliper off the rotor you can sometimes detect the in & out movement by bolting a tireless rim to the hub and grasping that to push and pull at the hub (you can use a rim with a tire but it's harder to grasp and the tire flexes making it harder to detect movement from the hub). Any movement in or out is the bearing.

But unless I observed definate bearing movement I would install one of your old rear axles at a time and see if that eliminates the noise, if the noise disappears it's the new axles if not I would really start to suspect a bearing.

These sealed units last a long time but when the start to fail it's usually a steadily accelerated failure.