Audio downloaded from Firebase doesn't make noise Swift 4 - ios

Question

I am currently working on a code that downloads .m4a audio format files from Firebase and allows the user to hear the music play within the same View Controller. Through lots of research on SO and other websites, I managed to get the audio downloaded, but when the audio is supposed to be being played, I only hear static. In fact, it actually plays the entire duration of the audio clip (e.g. the audio is 6s long, so a user would hear static for exactly 6s), so I know for a fact it is actually downloading something, just nothing is playing.
Below is my source code for the download function and play music function. I tried searching this topic on SO, but there are very few articles pertaining to audio download to iOS from Firebase (mostly it seems to be "how to download images", etc.)
Thank you very much in advance!
Sam
//Function to start playing music
func playMusic(){
do {
self.audioPlay = try AVAudioPlayer(contentsOf: self.localSongURL)
self.audioPlay.delegate = self
self.audioPlay.prepareToPlay()
self.audioPlay.play()
self.audioPlay.volume = 1.0 //I tried adjusting volumes to see if it would make a difference
} catch {
createAlert(title: "File Not Found", message: "Audio downloaded cannot be interpereted.")
}
}
//Function to download music
//In the Firebase storage, songs are listed underneath an ID, so the "tillAt"s help to parse through
//the appropriate strings to get the right path for collection
func downloadMusic(){
let tillAt1 = self.songPath.components(separatedBy: ID + "/")
let tillAt2 = tillAt1[1].components(separatedBy: ".")
store = Storage.storage().reference().child(patientID).child(tillAt1[1])
//From here is where I think the issue is within
self.localSongURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent(tillAt2[0] + ".m4a")
store.getData(maxSize: 128 * 1024 * 1024, completion: {(data, error) in
if let error = error {
print("Error Here _______________ Level 1")
print(error)
} else {
if let d = data {
do {
try d.write(to: self.localSongURL)
} catch {
print("Error Here _______________ Level 2")
print(error)
}
}
}
})
}