My HTC M8 has started ringing when I try to turn it off. How can I stop this?

[AC Question]

Have I accidentally changed the settings?

 

[B. Diddy]

Welcome to Android Central! Do you mean the ringtone sounded while turning the phone off? Were you powering off completely, or just pressing Power to put the screen to sleep? Did the ringtone stop on its own, or continue?