Hi.
Just to confirm you have checked that your user is in the audio group?
Can you let me know if you are using gnome or kde ? Also are you running 32 or 64 bit ?
I take it you have sound in your general desktop ?
Try and also make sure you have the following packages installed (not all of these will be relevant but there is no harm installing them )
sudo apt-get alsa-utils alsa-oss linux-sound-base libsdl1.2debian-alsa oss-compat
Also if you are using KDE (which is so advisable imo) change the auto-suspend time to 1 sec.
(not much experience with gnome... but i understand the gstreamer plugins are important ?)
I would also backup your paintball2 folder and try and extract a fresh copy to test - also try the different sample rates - i.e 22 or 48 - after changing close the game and restart...
As this sounds like a general oss sound issue for you , you could also try posting at
http://ubuntuforums.org(I had the same issue with ubuntu (it's always Ubuntu that has these stupid issues....) with enemy territory but that was fixed by installing
libsdl1.2debian-alsa
If you get nowhere let me know, I will attempt to install what ever version of Ubuntu you are using and try to recreate your issue (not presently running Ubuntu - running opensuse and gentoo - I find all *buntu variants very buggy)