I have a Motorola Moto E 2nd Edition running Android 6.0.1 (Marshmallow) and CyanogenMod 13.0. I get a chirping sound whenever I plug or unplug the USB connector. This behavior started recently, when I was having some problems with my SD card. What setting controls this behavior? If the chirping is warning me about something, what is it warning me about? I can't find anything in the settings either for Notifications or for Sounds. It seems that on some phones, "Sounds and Notifications" is a single set of settings -- but not on mine.
It seems that the chirping is activated by the setting "Charging Sounds / Enable", and plugging/unplugging the USB cable activates/deactivates charging through the cable. Disabling that setting turns off the chirping.
So apparently the chirping has nothing to do with the SD card.The chirping sound itself seems be hardwired and not able to be changed, although it might just be that no one here has discovered the way to change it. To confuse matters further, if I turn on the charging sounds and plug in a pure USB power cable (the kind that connects to a wall socket via a transformer), there's no sound.