What version of Premiere Elements and what computer operating system is involved?
There is a known issue with especially Premiere Elements 12/12.1 where the sound from unnumbered audio tracks and Soundtrack is lost when narration from the Narration Tool is added to the project.
The ID Llamadude found a fix for the issue. The background on this matter and the description of the Llamadude fix can be found
If worse comes to worse, you can create your narration clip in a free program such as Audacity, and then import that narration clip (wav) into the Premiere Elements project with Premiere Elements Get Media/Add Media/Files and Folder. Llamadude's suggested fix should resolve the issue. It has for many.
Looking forward to your results.