Nobody can tell you anything without exact info about your source file, version of PS, your system, audio settings.
Can you paste a screen shot of your timeline to this thread please? Or the entire workspace if it is easier.
Yep, it doesn't appear to be there, but it is odd that you can hear it. Just to make sure, move the timeline up, and un-twirl the video track options to make more room, and make sure the audio is not hidden.
If there is definitely no audio track, install Handbrake, which no video editor should be without. Note: I don't know if Handbrake is available for Mac.
Run the original file through Handbrake setting the output to MP4 and audio to MP3. This will get you past any issues with unsupported CODECs. Please let us know how you get on.
What you are showing is normal in Photoshop for a video with embedded audio. If you click at the top right of the clip in the timeline you will see the audio controls.
The separate audio track is for adding additional audio.
If you need to separate the audio - either use handbrake as suggested by Trevor or use a proper video editor like Premiere Pro
Ahhh I've learned something.
I never use Photoshop for video though, and it's inability to display the audio wave makes it close to useless IMO. Proshow Gold is way better for syncing sound to picture. In fact Proshow is even better than Premiere Pro in this respect.