I am runnint QT 7.0 and for some reason now the audio is all screwed up. I seems sound like an echo. I went home on Friday and when I came back on Monday it didn't work. I uninstalled iTunes and QT and re installed QT and still nothing.
Have you checked the sound output options in Quicktime?Edit>Preferences>Quicktime Preferences. From the dropdown list choose "Sound Out". and see what the option for "Choose a Device For Playback" is. You should also have the Options of "DirectSound" and "WaveOut" as well as rates and such.
Might want to check the same in windows.
Control panel>Sounds & Audio>Audio tab.