Originally Posted by dabac

Freewheel(and cassettes too for that matter) can often wobble around a little. For freewheel there are at least two fairly obvious contributors:
1) bearing play is set by shims, so getting it just right isn't that easy. Since a little play during freewheeling isn't hurting performance it's usually tolerated.
2) the thread for the freewheel may not be "perfectly" aligned with the wheel axle. Once again, with negligible impact on performance it's tolerated.