When you receive an email or a reminder goes off in Outlook, a sound plays. Here's how to turn off the sounds in Outlook: 

Outlook 2003 & 2007

1. In Outlook, go to the Tools menu and select Options.
2. On the Preferences tab, click E-mail Options.
3. Click Advanced E-mail Options.
4. Uncheck Play a sound.
5. Click OK twice.
6. Back on the main Options screen, switch to the Other tab.
7. Click Advanced Options.
8. Click Reminder Options.
9. Uncheck Play reminder sound.
10. Click OK three times to close all windows.