Thermal convection has a lot to do with the process. This is not a quite accurate depiction, but uneven heating of many objects naturally “crack” like bread in an oven.
Earthquakes are a factor, but to my knowledge not the driving factor. Pressure buildup between plates pushes them against other plates with less pressure. Sound is a side effect of a ball hitting a surface, and earthquakes as far as I know are secondary effects cause by magma pressure buildup.