The Push IO Manager will play any sound included in the GCM payload, so long as the sound you're playing is in res/raw folder of your project.
More information about sending these sounds can be found in the Server API topic.
NOTE: Unlike iOS, payloads that contain sound for Android do not need the filetype (.wav or .caf, etc.) to be present in the payload. For example, a sound file "timeralarm.wav" will only need a payload of "sound":"timeralarm" to play on your Android device.
For Android, two default notification icons can be set (Android 3.0+):
[1.] The Small Icon is the icon displayed in the Status Bar:
[2.]The Large Icon is the icon displayed when you pull down the Notification Drawer:
These images are taken from the drawable files of your resources (res) folder.