A search of this topic hasn't revealed anyone else having my particular problem.
I downloaded through RapidShare, opened the .rar files, which combined into one .mkv file. Got the necessary add-on to allow QuickTime to play a .mkv file.
Then I had a wonderful time watching ANH in a very enjoyable way.
Yesterday I try playing it again, and the sound is dubbed! Nothing I tried in QuickTime made any difference. What is going on?