Sounds like you may have more than one instance of the XAudio2 object.
Run debug layout and click on XAudio2 to see how many instances you have.
If you have more than one, then you will want to remove the extras.
Since you cannot select only one instance to delete, you will have to delete the XAudio2 object then re-add it. Or, if you have lots of sound events and don't want to re-add them all, do this:
1. Give XAudio2 the destroy on start attribute.
2. Add an event to create a XAudio2 at the start of the layout.
hope that helps.