Cracking sound when press lock button on iPhone Xr

Came across the issue on the second day after buying the new phone. After some time of not using the phone, the first time I press the Lock button it makes a cracking sound. As if there’s something inside out of its place.

The following next times I press the Lock button it sounds normally. After 10-15 mins the phone lies still on the table the first press once again makes a cracking sound.

Has anyone came across this issue? Previously had the same on iPhone 7 but after 1y using it.