I heard/seen that some single phase motors can cause surface finish issues like that, something to do with the phase voltage timing and doesn't occur with 3 phase motors. I don't know much about AC motors so maybe someone can chime in if it's true.
Happened with my lathe but I only got it when facing alumnium at certain speeds. I never seen or noticed it with any other materials though. Couldn't actually feel the pattern with my finger nail. If I ran the belts loose it got much better, as in didn't get it nearly as much. I later switched to link belts & it completely went away.