Q How I can stop my Mac making its startup sound?

A If you are happy with a muted Mac, turning the volume to zero should also silence the startup chime.

However if you just want to start up in silence, then resume normal audio volume, you will need to be a bit more ingenious. There is a shareware app, Startup Chime Stopper, and a couple of cheap apps in the App Store (Silent Start and Silent Boot) which can do this for you. The more capable general utilities, such as MacPilot, also offer the option.

The cheapest solution might be to find an old stereo headphone jack. Insert that into the Headphone output socket whenever you want to mute your Mac, and remove it to restore normal sound. This works because inserting the jack automatically mutes output to internal speakers.