A Sound Plays When You Plug In the Charger
On a MacBook, a connection chime can play when you connect the charger, even if the speaker is muted.
You can verify this by playing connect_power.aif under /System/Library/CoreServices/PowerChime.app/Contents/Resources.
The setting to stop this sound on charger connect is simple.
Run defaults write com.apple.PowerChime ChimeOnAllHardware -bool false;killall PowerChime in Terminal.
$ defaults write com.apple.PowerChime ChimeOnAllHardware -bool false;killall PowerChime
To enable the chime again, run the following command in Terminal.
$ defaults write com.apple.PowerChime ChimeOnAllHardware -bool true; open /System/Library/CoreServices/PowerChime.app &