I know this is an old topic, but I recently ran across this and had trouble with it myself. I have a 2015 Tahoe LT with the HMI 2.5 module that has CarPlay/AndroidAuto.
For me, setting chime on the *lowest* value did not work. I had to set it on the “2” in order to get a very low (normal) door chime.
Ignition must be in on/accessory to access the Vehicle radio option. I’ve attached some pics to show how I accessed it and what my current settings are. Anything lower results in a very loud chime, which kind of goes against how +/- works, but ??
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