Welcome to the JavaRanch, Dieter!
The log message indicates that the webapp is creating a Thread that it does not destroy. In addition to obstructing Tomcat's ability to terminate itself cleanly, it also indicates a possible bug (or at least careless programming) in the application. Please note that in any event no HttpServlet function may spawn a thread. Not only is it a violation of the
J2EE standards, but it can potentially corrupt Tomcat itself.
I'm not sure how you intend to play a sound. If you literally code a sound-playing function in your webapp, the sound cannot be heard on the client machine, because the server will be playing it through whatever audio channels the server machine itself has available. And server machines are rarely hooked up to loudspeakers.
To get a server-generated sound to play on a client you would have to respond to the
servlet request with an audio data stream. Specifically, it would have to be encoded with a MIME type for one of the media forms that the client machine can play.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.