Below are steps you can take to troubleshoot your OneNote audio not playing in a recording:

1. Check that the audio device on your computer is working properly.
2. If the issue persists, try recording audio from a different audio device.
3. Ensure that the recording device is properly installed with the latest version of its respective driver.
4. If the issue still persists, reset the audio device settings and try recording audio again.
5. Check the volume levels of the device.
6. If the issue is still not resolved, restart your computer.