Sound system of Mac book pro

Reset PRAM:  Reset NVRAM or PRAM on your Mac - Apple Support

Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, and recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac.

Reset  SMC:   How to reset the SMC of your Mac - Apple Support   Choose the appropriate method.

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Resetting the system management controller (SMC) can resolve certain issues related to power, battery, fans, and other features.

If the internal speakers on your Mac aren't working