This afternoon I started becoming increasingly frustrated by the fact that all of my GTK applications make noises upon mouse click. A couple prevalent examples of this are Firefox and Chromium-Browser. In each case, adding a new tab, or clicking refresh, made a small "dunk" sound. The sound has always been there, but I wanted to focus on the audio I was listening to. I began looking through preferences, and it seemed that there was no way to make this sound go away. Google searches for Gnome/gtk mouse click sound weren't very helpful either.
Eventually, I found a way to eliminate these small annoying noises for good. I needed to add the following to my ~/.gtkrc-2.0-kde4 file:
And restart any running Gnome/GTK applications, and the annoying sounds are gone! I hope this helps others experiencing this issue.