Heh, old thread, but I ran into this issue today and found the solution. Put these two lines in the ~/.gtkrc-2.0 file:
Turns out this is an issue with GTK+ apps (like Firefox) that try to connect to port 4713, the PulseAudio port. Since I don't have PulseAudio installed, those socket connections failed. I normally run Firefox from a menu, so I never saw those error messages. Only today when I was running Firefox from the command line did I notice it.
The bigger issue is why on earth are GTK+ apps trying to use sound when clicking on various menus (like the Tools menu in Firefox)? That's ridiculous.