There is a click like sound when locking or unlocking your HTC 10. If this sound is annoying, do as follows to disable and turn off screen lock sound on HTC 10, do as follows:
1. Open the Settings app
2. Scroll down to the Phone settings and touch to open the Sound & Notification settings
3. Scroll down again to System settings, and here make sure the Screen Lock Sounds option is unmarked.
4. From now on, no sound will be played when locking or unlocking your HTC 10