World of Warcraft\Data\itIT\Sound\Spells\FizzleCreate five zero bite .wav files, named as follows:FizzleFireA.wav
FizzleFrostA.wav
FizzleShadowA.wav
FizzleHolyA.wav
FizzleNatureA.wavThis will remove the 'fizzle' sounds associated with each element of attack when a spell fails to cast.I'm not sure what element
If you want instead to remove the 'tick' registering noise that occurs, create this zero byte file:
Sound\Interface\uEscapeScreenOpen.wavThere may be alternate fizzles for warriors, I'm unsure.
If none of the above fizzles work then one of these should:
uChatScrollButton.wav
iUiInterfaceButtonA.wav
uEscapeScreenClose.wavNote that muting any of these latter ones will affect other parts of your UI.