You could have downloaded StartupChimeMute 2.1.7 for Mac from our software library for free. This Mac app was originally developed by atalantia. The application lies within System Tools, more precisely System Optimization.
From the developer:
StartupChimeMute mutes the startup chime on OS X. The process can also be undone with the included deinstaller. The application is not required to run after installation.
You may want to check out more software for Mac, such as Dock Delight, which might be similar to StartupChimeMute.