Comment 9 for bug 456273

likewise I think it started yesterday for me. it looks like the most recently updated gstreamer package is gst-plugins-good0.10, from Monday:

gst-plugins-good0.10 (0.10.16-1ubuntu3) karmic; urgency=low

  * backported debian change:
  * debian/patches/000{1,2}-equalizer*.patch:
    + Patches from upstream GIT to fix equalizer in stereo mode and
      to use better filters for the first and last band.
  * debian/patches/00[1-20]-pulse*.patch:
    + Patches from upstream GIT to improve PulseAudio plugin and fix
      some major issues, like decreasing the volume after every track
      in some cases.
  * debian/patches/70_latency_update_returns_null.patch:
    - the change is in the new version

 -- Sebastien Bacher <email address hidden> Mon, 19 Oct 2009 10:31:24 +0200

This seems like it might be the place to look, particularly the pulseaudio stuff?