Where are "available offline" Dropbox files and folders stored on Android devices?

Thanks for the update David K.124! 

First off all, note that making a file “Available offline” makes a local copy of your file within our mobile app. The file can be then viewed offline and will sync with Dropbox. If any changes are made to the file while you are offline, the changes will be synced once your device is connected to Wi-Fi.

On Android, you can make a file “Available offline” by following these steps:

- Open the Dropbox app and navigate to the file you want to make available for offline access.
- Tap the arrow to the right of the file name
- Toggle the switch next to “Available offline” on (green).

You can find out where all of the files you have made available offline by tapping the menu button and selecting “Offline files” to open the folder.

Could you try exporting the MP3 file from the Offline Files or Home view now and let me know if this persists? You should be able to see "export" option for MP3 files as well after pressing the ellipsis button (...) so if this is still not happening please send me a screenshot so I can have a visual of this as well. 

Thanks for your patience and cooperation again David. Please let me know if this worked for you.