If you are looking for this specific file, it is likely stored in one of two places on your device:
When you send an MP3 through WhatsApp, the app often renames it to this standardized format to maintain its internal database. If the original file had (like artist or song title), your music player might still show the "real" name, but the file itself will keep the AUD-20200709-WA0020 label in your storage. Download AUD 20200709 WA0020 mp3
: Indicates this is an audio file (rather than a voice note, which typically starts with "PTT"). If you are looking for this specific file,
: The unique identifier for that day. WA stands for WhatsApp, and 0020 means it was the 21st audio file (starting from 0000) processed on that specific date. Where to Find and Download It : The unique identifier for that day
To keep the original filename when sending audio in the future, you can send the file as a instead of an Audio file.