When you receive a chat, you are notified audibly with a sound notification. Sound notifications are enabled by default in Gmail and orkut. Of course, you can always disable them at any time. Here's how:
- Click the gear icon link at the top of any Gmail page, and choose Settings.
- Click the "Chat" tab.
- In the Sounds section, select Sounds off.
- Click Save Changes.
You must have Flash enabled on your computer to use sound notifications in Gmail.