dpb wrote:
....

I'd take it apart enough to make sure it's the axial movement that's the
problem (hitting on either end, not the sides) and if so, just add an
appropriate thickness of nylon washer(s) to take up enough of the end
play to stop it.

Of course, be sure to only add sufficient to stop whatever is hitting,
don't add enough to make the shaft hard to turn...

Oh, one other thought -- it's possible particularly if it is a squirrel
cage fan the fan itself has moved on the shaft or simply needs to be
adjusted a little in one direction or the other.

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