Fedora Core (up to core2 test2 at least) comes with muted sound controls.
If you have alsa-tools installed, you can run alsamixer to adjust the volume. In KDE you can do the same thing (but much nicer) with kmix. There is a gnome app too, but I cant think of the name right now.
There can be other problems (I have, at times, wanted to silence the f*** thing for ever, until I realized this was the very thing I wanted to cure
) , but this is the most likely
I hope this helps,