Oh, ok. It is a problem with JavaSound then. Oracle has royally screwed up JavaSound in recent versions by their decision to remove the "Java Sound Audio Engine" software mixer (requiring developers to choose one of the hardware mixers, which are all different with different capabilities for different sound cards). I'm in the process of writing my own software mixer, but it will probably be some time before it is complete (I don't have much free time for programming any more, and what little I do have I am busy working on my N64 emulator project). In the mean time, I would suggest using OpenAL, as it is more reliable (used to be JavaSound was more reliable, but not any more).
For the native OpenAL library, it ships with LWJGL (which I assume your application is using since you are writing it for jPCT, unless you are going with the software renderer) It is included with all the other native libraries.