Playing the attached file and exploring metadata doesn't give any useful information. Lets open audio.wav via Audacity and look at its spectrogram:

Here we see that the spectrogram is divided into parts. In every part we can distinguish 8 levels. If consider them as bits, then every spectrogram part is a byte. Lets try to assemble binary code from the spectrogram reading each part from top to bottom and considering the spectral lines as 0 and the gaps as 1 (I just guessed it...): 01100110 01101100 01100001 01100111 01111011 01100010 01110010 01101111 01110111 01101110 01101001 01100101 01011111 01101001 01110011 01011111 01100001 01011111 01100111 01100101 01101110 01101001 01101111 01110011 01101001 01110100 01111001 01111101

Converted to ASCII: flag{brownie_is_a_geniosity}