What computer operating system is involved? Have you updated 13 to 13.1 for the Premiere Elements 13 Editor as well as Elements Organizer?
Please confirm if sound is lost for certain files in both Premiere Elements Editor and Elements Organizer?
What are the properties of these files? What is their source - same for sound and no sound?
When you import the file, do you allow for any conforming to complete before you do anything in the Timeline? For conforming, please watch for a progress bar in the bottom right of the workspace.
Please review, consider, and supply more details. Any questions or need clarification, please ask.