2013 Dodge Grand Caravan High Pitch Frequency FM Stereo

My wife bought this van used and she knew there was
an issue with the stereo having a high pitch frequency
on the FM band. The dealer tried to swap out the
stereo for another stock caravan stereo and there was
no change. It only does it on the FM band when a
station comes in clearly or mostly clearly. It doesn't
happen when playing a cd. It does it if it is in
accessory or with the ignition on and doesn't change
tone or pitch with acceleration. I have traced the
antenna cable back to the coupled point on the
passenger side floor/side panel all is connected
properly. I have traced the ground under and below
the glove box, it is good and metered at a consistent
.1 ohms. I looked at the connections from the antenna
to the board on the stereo even though I have doubts
it is the stereo itself given the dealer already tried a
swap. The soldered connections appear to be good
and meter a good connection on both the center pin
and shielding. I tried to swap antenna mast itself and
it did not change. I have tried to run the harness down
and bypass the first section of antenna cable by
hooking directly to where it is coupled on the
passenger side, no change. I am at a loss and
frustrated. For some reason the radio working is
important to my wife in 2024. Any insight would be
appreciated.