KDE uses a different sound engine than GNOME. It uses Phonon. I would start there. Go to Settings, System settings, Multimedia in the Hardware section and Phonon at the bottom. Click on backend.
Try switching from Gstreamer to Xine. Sometimes Gstreamer and PulseAudio do not work well with some sound cards and Xine gives better results. Many GNOME users get better results by installing Totem-xine than using the default Totem with Gstreamer. It is easy to switch back if you don't like it. You may have to logout and back in for that setting to take effect.
If it is already Xine then you can try Gstreamer in the same way.