No sound in remote push notifications

Greetings,

in the past I did my best to get notification sounds for push notifications working but with no success.

On the client side I'm using WindowsAzure.Messaging (https://components.xamarin.com/gettingstarted/azure-messaging) to handle push notifications on iOS and Android. Everything works fine except the sound.

I'm sending notifications from PHP with the following code:

if ($plattform == "apple")
    {
        $alert = '{
        "aps":{
            "alert":{
                "title":"Neue Abholer vorhanden",
                "subtitle":"Es liegen ' . $_POST['anzahl_abholer'] . ' neue Abholer bereit.",
                "body":"Hier tippen um Vegvisir zu öffnen",
                "sound":"default"
            },
            "badge":'. $_POST['anzahl_abholer'] . '
        }
    }';
    $notification = new Notification($plattform, $alert);
    $hub->sendNotification($notification, $gcm_id);
    }
    else if ($plattform == "gcm")
    {
        $message = '{"data":{"message":"Es liegen ' . $_POST['anzahl_abholer'] . ' neue Abholer bereit!" }}';
        $notification = new Notification("gcm", $message);
        $hub->sendNotification($notification, $gcm_id);
    }

And locally on iOS:

FinishedLaunching:

        if (UIDevice.CurrentDevice.CheckSystemVersion (8, 0)) {
                        var pushSettings = UIUserNotificationSettings.GetSettingsForTypes(
                        UIUserNotificationType.Alert | UIUserNotificationType.Badge | UIUserNotificationType.Sound,
                        new NSSet());

                    UIApplication.SharedApplication.RegisterUserNotificationSettings (pushSettings);
                             UIApplication.SharedApplication.RegisterForRemoteNotifications ();
                         } else {
                        UIRemoteNotificationType notificationTypes = UIRemoteNotificationType.Alert | UIRemoteNotificationType.Badge | UIRemoteNotificationType.Sound;
                    UIApplication.SharedApplication.RegisterForRemoteNotificationTypes (notificationTypes);
                         }

public override void ReceivedRemoteNotification(UIApplication application, NSDictionary userInfo)
        {
            ProcessNotification(userInfo, false);
        }

        void ProcessNotification(NSDictionary options, bool fromFinishedLaunching)
        {
            // Check to see if the dictionary has the aps key.  This is the notification payload you would have sent
            if (null != options && options.ContainsKey(new NSString("aps")))
            {
                //Get the aps dictionary
                NSDictionary aps = options.ObjectForKey(new NSString("aps")) as NSDictionary;

                string alert = string.Empty;

                //Extract the alert text
                // NOTE: If you're using the simple alert by just specifying
                // "  aps:{alert:"alert msg here"}  ", this will work fine.
                // But if you're using a complex alert with Localization keys, etc.,
                // your "alert" object from the aps dictionary will be another NSDictionary.
                // Basically the JSON gets dumped right into a NSDictionary,
                // so keep that in mind.
                try
                {
                    if (aps.ContainsKey(new NSString("alert")))
                    alert = (aps[new NSString("alert")] as NSString).ToString();
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }


                //If this came from the ReceivedRemoteNotification while the app was running,
                // we of course need to manually process things like the sound, badge, and alert.
                if (!fromFinishedLaunching)
                {
                    //Manually show an alert
                    if (!string.IsNullOrEmpty(alert))
                    {
                        UIAlertView avAlert = new UIAlertView("Notification", alert, null, "OK", null);
                        avAlert.Show();
                    }
                }
            }
         }