This bit of code works, but the sound only plays once per scene. Not exactly sure what is causing this, but it is most likely a problem with the node's properties. Here they are.
P.s: It is a .wav file and none of the import options are on.
The node options looks good. It might be some logic problem. Take a look in this code: https://github.com/Guizeronet/godot-platform-test/blob/master/obj/char/char.gd
You can download my example and see it running. It is different from my last comment, it can works better. (Download here: https://github.com/Guizeronet/godot-platform-test )