Apple presented different features in different versions of Mac. For its educational resellers Apple created the settings for Monitors & Sound together. The purpose of keeping them together is to hinder the users to change the settings. If any user tries to change it, it requires System AV extension to identify the other preferences. But unless the Monitor & Sounds Control Panel is opened, System AV file cannot do anything in the presence of Display or Sound Preferences.
The development team at Apple has created the Monitors & Sound Control Panel in such a way that monitor Control Panel save its settings in the Display Preferences File and Sound Control Panel saves its settings in the Sound Preferences file. Both of these files are stored in the Preferences folder as Monitor & Sound Preferences.
To fix the self-muting sound in Mac, open the folder of Preferences and delete the files of Sound Preferences and Display Preferences because by default the operating system searches for these two files. With this, you will surely be able to fix the self-muting sound. Apple incorporated this feature only for educational reseller; none of any other Mac has this feature.