I picked a song for an alarm and now every alarm that I create with Siri uses that song. I cannot change the default alarm song back to the default alarm sound. When I need to create an alarm manually I can see the default alarm sound, but every single time I create an alarm with Siri then it reverts back to that one song. It's impossible to change the default alarm sound that Siri uses. I'm using iOS 10.2.
I had the same issue. Did a hard reset (power and volume down until the Apple logo appeared. That'd be power and home button for all other non-7 devices.) It fixed the problem. It was driving me absolutely crazy.