Samsung
Turn Screen Lock/Unlock Sound On or Off auf Samsung
Samsung phones play a short lock and unlock tone whenever the screen switches state, independent of your ringtone or notification sound.
The sound comes from the general system sound controller, which also handles tap tones, charging beeps and other feedback sounds. It fires every time you press the power button or the screen times out, which is why it often feels more frequent than actual notifications.
You can turn it off completely, but Samsung does not offer a way to swap it for a different tone or file. The switch only toggles the sound on or off; there is no volume slider or sound picker attached to it.
To disable it: Settings ➔ Sounds and vibration ➔ System sound/vibration control ➔ turn off Screen lock/unlock.
If you still hear a click after disabling this option, check whether Touch sounds or Media volume is causing a separate tap sound, since those are controlled independently from the lock screen tone.