Audio disappears

My college has closed captioned videos for me and gave me DVDs.  I want to upload them for my my online class.  The problem I have, is that the files are in 15 minute segments and I want to link them back up into 1 hour videos.

I have converted the files to MPEG4.  The files play fine on my computer (Macbook Pro with Catalina 10.15.7).  When I load them into Rush, the Audio files seem to dissapear.  There is no sound when I try to play them back.  Any suggestions would be appreciated.

I have also tried loading directly from DVD to Premier Pro and have the same problem.