Choose or disable the alert sound
Your computer will play a simple alert sound for certain types of messages and events. You can choose different sound clips for alerts, set the alert volume independently of your system volume, or disable alert sounds entirely.
Click the sound menu in the menu bar and click Sound Settings.
On the Sound Effects tab, select an alert sound. Each sound will play when you click on it so you can hear how it sounds.
Use the volume slider on the Sound Effects tab to set the volume of the alert sound. This won't affect the volume of your music, movies, or other sound files.
To disable alert sounds entirely, just select Mute next to Alert volume.