A couple of questions:
1 - is there a variable speed control on the fan?
2 - if not, is it a pull-chain multispeed fan?
3 - are you on the same pole pig? Being 500 yards away,
probably not, but......
If there is a variable speed control, it is most likely the
culprit. They operate such that they vary the AC to the
fan. Generally this is done with a SCR-type semiconductor
and the switching edges can generate a lot of HF/VHF noise.
If the owner installed the fan and speed control, I'd bet
that the AC ground is not hooked up, especially if it is an
older house with 2-wire distribution.
If you are on friendly terms with the owner, check the
wiring. If not, you should be able to get the local
electric utility to check it out.
I doubt if anything other than grounding and/or shielding
the speed control will help the noise. If it is the speed
control and you can't ground or shield it, see if there
is a possibility of putting the fan on a variac-type
AC speed control which does not generate switching
transients.
Good luck.......Jim