Hello there thebehaviorist,
Thanks for posting in the Apple Support Communities.
Check out the suggestions below to see if this changes what you're experiencing. You can locate additional information here: If you can’t hear sound from your Mac speakers - Apple Support
If you’re trying to listen through your computer’s built-in speakers
1. Unplug any headphones or external speakers.
2. On your Mac, choose Apple menu
> System Preferences, click Sound
, then click Output. Make sure “Internal Speakers” is selected, the “Output volume” slider is not all the way to the left, and the Mute checkbox is not selected.
Be sure you're up-to-date with the latest macOS version as well as any updates from the App Store to see if that may clear this up as well.
If this is only occurring when using Duolingo, have you worked with Duolingo Support to see what could be causing this to occur? If you have already done that, Contact Apple Support to check into this in more detail with you.
Have a great day!