Oh, wait. One more. You could have a Sound File From Hell. If you have a sound file where the Left and Right tracks are recorded out of phase, it’s terrifically hard to sort what happened while you’re listening in stereo—two track, two speakers, etc. But the instant you listen in mono-mix, all sorts of nasty things happen including having the show vanish. It could certainly account for muffled sound and distortion—only under certain conditions.
Is it a stereo track—two blue waves? Use the left-hand menu system > Split Stereo Track. Select one track of the split by clicking just right of the up arrow and Effect > Invert. Menu of the top track > Make stereo track.
Problem gone?
If it is, we should track this back to the maker and find out what’s causing it. This isn’t an Audacity problem other than it may be configured to reveal the error. There are perfectly innocent-looking microphone adapters which can do this.
https://forum.audacityteam.org/t/devils-adapter/46592/1
Of course, it’s also a given you’re listening in mono, not stereo. So that could be a surprise. This could happen if you’re listening via a very fancy gaming system that likes to “improve the sound to help you.”
Koz