Wow, I was just about to post the same topic. I'm having the same problem. It started some days ago, and I have yet to find a solution. If I restart or log out and start playing a audio-file before opening any other applications it works. However, after a couple of hours, especially If I have a track paused, the problem seems to reoccur. So I have to do the same thing over again, pretty annoying.
For me the track gets stuck at 00.00 (or if I've paused a track and then try to resume it after a couple of hours, it just drops down to 00.00 and gets stuck), and after a couple of seconds the application freezes. Takes a couple of seconds more, then it unfreezes, but as soon as I try to play a audio-file this happens again. This problems occurs in every audio-playing application I've tried. Amarok, Rythmbox, Audacious, it happens to them all. So I guess it's not a problem with any of those applications, but rather concerning a codec or something?
Help would be greatly appreciated.