I think its pretty hard for a fan's brush noise at a couple of kHz to
reach up to the Av band.
Here's another possibility:
Over time your ground connections are oxidizing and increasing
resistance. The noise may well
be due to normal radiation of digital circuit clock and switching. Check
to see if there is a voltage greater
than a few millivolse between both your radio and GPS ground pins to the
main battery negative terminal.
If there is, improve the connections, protect them and add copper to
reduce path resistance.
No oxidizing connections would include FastOns or solder, but ring
terminals often rot.
Ira N224XS
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