The natural expansion and contraction of wood can cause nails to move or "pop" out of place. The nails can usually be reset.

A phenomenon found with load-bearing walls, posts and structures, in which the building has settled. Occasionally, the pressure from the settling will force out the heads of any nails that have been driven into such load-bearing structures.

When the structure of a new home settles, nails in the load-bearing parts tend to pop out slightly.

Nails that come loose from a stud and push joint compound up. Caused by normal wood shrinkage and home settlement.