"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley
in . 3.70:

There should be some axial play. Those are simple thrust bearings.
"Rattles" don't come from axial play, unless it runs so fast it lifts
the fan up by aerodynamic force (not likely).


BTW... if that's what causing it, try reversing the fan. If it does NOT
rattle in that direction, that's the likely cause. In that case, clean the
bearings and add a spacer washer. They usually come apart very easily,
generally with a keeper nut or external retainer rings.

Lloyd