Here are some troubleshooting steps if you aren't hearing audio.
The first and most simple reason could be that your video player volume has been turned down. The volume controls can be found in different locations, depending on the video source.
Primary Video Source
For the primary source, Vimeo, you can find the volume controls at the bottom right of the player next to the settings gear. The control is a small speaker icon. If you mouse over it, a slider will appear. The higher up the slider is, the higher the volume.
Alternate Video Source
For the alternate video player, Sproutvideo, you can find the volume controls at the bottom left next to the play button. This is the small speaker icon and when you mouse over it, a vertical slider bar will appear. The higher the dot on the bar, the greater the volume.
You can also click on the speaker to toggle mute on the video.
One reason you could be experiencing volume issues is if the site is muted. You can do this by right-clicking on the tab and looking for 'unmute site'.
If you see this, click on unmute site.