Here is a solution that comes to us via email that should work for the Java Web Start client (but not the applet):

Edit the shortcut or command that starts CGoban and add
-J-Dsun.sound.useNewAudioEngine="false"
after javaws.

For example, if your command was javaws cgoban.jnlp change it to javaws -J-Dsun.sound.useNewAudioEngine="false" cgoban.jnlp


Some of you please try this, and post the results here.

For those of you who use the "java" command instead of the "javaws", remove the "-J" For example,
java -Dsun.sound.useNewAudioEngine="false" -jar cgoban.jar

Thank you, person that sent the email.
(I guess he wishes to remain anonymous, since he did not post that here himself.)