hear it all the time, maybe more with 1ph loads than 3 ph, but since conductors do vibrate with a load on them anyway, I don't concern myself with it unless the rattling is excessive
I do know that some of them have been in service for more the ten years with no problems.and I would suggest that any vibration problems show up at the terminations and not inside a pipe, unless somebody forgot to ream the ends , as you wrote
I have also seen raceways that had disintegrated long ago with the exposed wires still looped through a coupling, outside, in the weather just humming along