Quicktime MOV no audio (just hiss)

I have a new Windows 10 PC with quicktime installed. I have some QT mov files (video with sound) that I viewed on on other PCs. When I attempted to view these .MOV files on the new Windows 10 PC, there is no audio, just a loud "hiss". I attempted to open the .MOV files in other applications (Sound Forge) and received an error message that said "Quicktime did not install properly, please reinstall quicktime". I reinstalled Quicktime. After that, the first time I opened a .MOV file in the QT player, it played with audio. After I closed QT, and opened another .MOV, the loud "hiss" problem returned (and has not gone away). At this stage when I open the .MOV files in Sound Forge (or Adobe products) I can hear the audio, but the audio will not play in basic applications (like the Quicktime player or Windows Media player) - just a loud hiss. There is nothing special about these .MOV files (they are from a Canon camera which I have used for years and viewed on many PCs).

Any ideas on how to get the audio codec working properly?