What commonly causes hardwood floors to squeak and creak?

Hardwood floors squeak primarily due to movement at the subfloor or joists beneath the surface. Loose nails, shifting boards, or gaps between the subfloor and joists allow flexing that generates noise when you walk. This structural movement causes squeaks and nail pops. Addressing the fasteners by tightening joists and securing loose boards is essential to stop floor noise, as surface materials alone, including hardwood or LVP, cannot prevent squeaking.