What version of Premiere Elements on what computer operating system?
What are the details of your avi and mpg export files....Publish+Share or Share/Computer/AVI or MPEG...what preset is selected in the Presets field? Are you using the default setting for the selected preset or are you customizing the preset under its Advanced Button/Video Tab, Audio Tab, and Multiplexer Tab?
When you find the export on your computer hard drive, do you find two files for the same export or just one?
Where is this sound that you do not hear in the export....
b. Narration Track
c. Numbered Audio Track
Can all the Timeline audio tracks sound be heard before export?
What is the estimated file size and duration of the Timeline content that is exported. See bottom of export settings area.
Let us start here and then decide what next.