During the development of QuickTime 2.5, the QuickTime engineering team uncovered a few minor problems in Sound Manager 3.2 (which is integrated into System 7.5.3) that could affect QuickTime. So, a new version of Sound Manager, Sound Manager 3.2.1 was created and shipped with QuickTime 2.5.
If you are using QuickTime 2.5, you should have Sound Manager 3.2.1 installed. If you are running versions of QuickTime prior to 2.5, it shouldn't make a difference which version of Sound Manager is used since the problems only appear when QuickTime 2.5 are used.
For more information on how to get Sound Manager see the following article: