A video without audio does not always mean the original post was silent. Facebook can expose separate video and audio streams, and a downloader may only find one of them.
Why audio can be separate
Some Facebook videos and reels use separate streams for the visual track and the audio track.
If the public page exposes only the video stream, the downloaded MP4 can play silently even though the original post has sound.
Three tools to compare
Try another resolver if you need a combined file. Some tools may find a combined video while others show separate audio.
If the preview offers a separate audio button, download it too instead of assuming the video button contains sound.
What to check before retrying
Make sure your device is not muted and test the original Facebook post. Then check whether the downloader preview showed an audio action.
If you need one final file, you may need a tool that combines streams or a local editor after downloading both files.
When there is no fix
If Facebook does not expose the audio publicly, a downloader cannot invent it.
The cleanest fallback is to try the same public URL in another tool or choose a different source post.