I'd be very surprised if the bearings are replacable. I've
had enough window AC apart, they aren't really designed to
be serviced. Flush them out with solvent, and then use the
proper bearing lube is good. That is, "if" the OP has the
tools and repair skills to do so.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Bob F"
wrote in message ...


I would appreciate if anyone has any idea what might
cause this kind
of vibration in the fan and why it could just get better
on its own
without any service.


Reasonable guess is that the bearings in the fan need
oiling/greasing/replacing.

I agree completely. If you take apart the fan and remove the
bearings, A bearing
shop can sell you the replacements. It cost me less than $20
to do this on a
window A/C. If there are oil holes, oiling is the first
thing to try.