Hi Emily Johnston,
Welcome to Microsoft Q&A forum. I'm happy to help.
Please troubleshoot with following steps:
- Open Settings > System > Sound > Volume mixer > scroll down to Apps section > check the volume of your using browser.
- Hover the mouse to display area of YouTube > check the volume of YouTube video.
- Hover the mouse to display area of YouTube > check the video quality to see if the issue can be fixed with another quality setting.
- Test with another browser.
If you have any updates, please feel free to let me know.
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