Did you try muting the microphone and not the Wave? If your Mic is not listed in the volume controls, go to File -> Properties. (in the Mixer Dialog box)
You should then see a dialog box with some check boxes at the bottom. Scroll the list down (you might not have to scroll it if there isn't that many available devices) untill you see Mic/Microphone. Make sure it's checked and then click OK.
Then it should be there and you can mute it. That way you can mute the mic, but keep everything else!
...Or just unplug the mic when your not using it...which ever is easier for you.
