KDE 3.x uses the aRts sound system. In earlier versions there were a number of problems, but in recent years the only problem remaining seems to be that aRts hangs on to the sound system when it has finished with it. To cure this, use kcontrol > Sound & Multimedia. Towards the bottom of the General tab there is a setting for 'Auto-suspend if idle after:' Set this to 1 second.
That is not an error, but a configuration issue. To tell KDE 4 which soundcard to use (or prefer if available), call the application "systemsettings"