Well, nobody chimed in so I'll give you two cents worth.

If the noise really is coming from the fan and not a nearby loose bolt
(or the like),  I'd take it apart and see what I could see.  Might be
that the blade assembly is coming loose and rubbing on the radiator,
in which case it will eventually wear through and require replacement
of the radiator as well.  Or, like you say, it could be the bearings
inside the motor.  If it gets loose enough though it could still take
out the radiator. Or just seize up when you need it most.  Either way,
definitely something that needs looking into before it puts you on the
side of the road.

Good luck.

Harry

Ford FWD radiator fan/shroud assemblies are typically pretty failure
prone; I have seen a variety of failure modes.  I have even seen
harnesses overheat near the relay socket from overcurrent draw.  You
should consider replacing the assembly --- on the models I have seen
more recently, it is a complete assembly, fan, shroud, and motor, and
the price is not too bad (well, crap *is* cheap to make...)

Toyota MDT in MO