In game sound affects?

Definitely sounds like a common addon is causing that problem, Firstaïdkit. Try disabling your addons first. If that doesn't resolve it, please try the following steps:

Reset UI

For Windows XP/2000

1) Exit the World of Warcraft.
2) Inside the World of Warcraft Program Folder (default path is C:\Program Files\World of Warcraft) please delete the 'WTF,' 'Cache,' and 'Interface'
3) Restart your computer.
4) Make sure that you are using WOW.EXE or LAUNCHER.EXE to start the game. Do not reinstall any third party user interface modifications.
5) Upon launching the game, you should see the intro cinematic movie and be prompted to agree to the Terms of Use. Once you authenticate past the login screen, the 'AddOns' button should no longer be visible at the lower left corner of the character selection screen.

Both points mentioned previously must hold true if you should complete the aforementioned steps correctly.

Note: If you are on Vista you might need to find the Repair.exe file in your World of Warcraft folder, right click on it and 'Run as Administrator.' Then click all options and 'Reset and Check Files.'

Mac OS X

-Click on the desktop and then the Go menu on the top.
-Click Applications.
-Scroll down to World of Warcraft and select it.
-Right-click (Control+click if you own a 1-button mouse) on the Cache folder and select Move to Trash.
-Perform the above step for the Interface and WTF folder as well.
-Double-click the World of Warcraft application to launch the game and verify if the issue has been resolved.

Please do not run any UI installers or load any mods beforehand, as we want to eliminate them as part of the issue!