Cannot send Audio files on WhatsApp
WhatsApp (at-least the version 2.16.207 on Android version: 4.2.2 - JellyBean) doesn't seem to support audio files with WAV extension, I tried sending an mp3 and it seems to  work fine

However I found that WhatsApp with a same version on Andriod 6.0.1 (Marshmallow) has no problems in sending WAV files

In any case you can always use a WhatsApp File Sender as mentioned in this answer.