This is because dropbox is sending HTTP/1.1 302
redirect with header Content-Type: text/html; charset=utf-8
instead of HTTP/1.1 200 OK
with Content-Type: audio/mpeg
header.
Host your mp3 file on a http server so it is downloaded directly.
Or you can use following link. But this url pattern is not guaranteed.
https://dl.dropboxusercontent.com/s/bhowc21p2bzug70/NorthAustinNmeNEW.mp3