I occasionally, and randomly, arrive at an adjusted BB or hub that makes sounds like the balls rattling around, and clinking against on another.

This isn't bearing roughness, the bearings are very smooth, and there's fresh grease there that would also be expected to keep things quiet.

And no, there isn't a ball missing, however this occurs only when there is no retainer, and with a quite-full compliment of balls in each raceway.

I write it off as harmless. Perhaps thicker grease would make things quieter, or perhaps just a bit more tension on the bearing adjustment.

I have pulled apart assemblies because of the noise, only to find all is in order. Frustrating to say the least.

As for the Stronglight cups, the metal is good, but the octagonal wrenching flats are shorter and much more prone to slipping than the flats on typical hexagonal or twin-flatted fixed cups. And there are no 4-sided or 8-sided sockets available to help with home rebuilds.
Perhaps someone should make a run of 38mm Octo-shaped wrenches, wrought from 1/8" steel stock?