In **KDE 4.10.5** , you can disable all system sounds without muting all media.
`System Settings` > `Common Appearance and Behaviour` > `Application and System Notifications` > `Manage Notifications` > `Player Settings` > `No audio output`.
Also, you may **disable Event Sounds** : left click the sound tray icon and slide down the Event Sounds slider or completely mute it.
 plasmoid, and turn down "Event Sounds", similarly to the screenshot above.
If this doesn't work, you can turn off the sounds for each notification class individually, in `System Settings` > `Notifications`. Cycle through `Event source`, looking for entries with the `Play a sound` icon associated with the entry, then toggle off `Play a sound`.