I solved the problem. I was WAY off track with the whole natives discussion.
SOLUTION (IMPORTANT FOR ANYONE USING SOUND IN THEIR APPLET!):
Sound must not be initialized in an applet's init() method!Simply moving the code out of the init() method fixed it. Yes ... it was that simple. Probably a thread issue, couldn't say.
you should blame your own code before the library you are using
Sound advice, oh wise javalwjgl ...