Why does the text message vibrate without sound?

First find the Settings icon on the home screen, and then click Open.

Find the "Sound" option in the settings list and click Enter.

Locate the Lock Sound option in the sound settings list.

Then turn Lock Sound off and on again. Then please try to press the power lock button of Apple's mobile phone to confirm whether there is a lock sound.

If you turn off the button sound in the settings and then turn it on again, there is still no sound. Next, please press and hold the "power lock key" on the top of the phone until the sliding shutdown screen appears, and then slide to shut down.

Wait until the shutdown is successful, then press the "power lock button" on the top of the phone to restart, and finally try to lock the screen to confirm whether there is sound.