Just wanted to post for anyone that stil has this problem.
I updated to 9b and it fixed my no sound problem after importing video from a dvd (mpg files). Worked cleanly for me!

Copied from another post:

Just go to --> http://www.sonycreativesoftware.com/download/updates/moviestudiope
Make sure 9.0b is selected on the dropdown list and click "download". Then install it over the existing version. No need to uninstall.

mike_in_nc