does not always mean foundation, could also be framing settling or changing.
Look for: Doors not closing windows not closing or tight. Cracks above doors interior and exterior. Brick cracking on the outside. Chipping away of slab foundation on corners. Cracks in ceiling. Pipes breaking inside the foundation Water on exterior of home in puddles
** all homes even under ideal conditions will settle to an extent, especially new homes. But, drastic settling can cause real problems.