What’s going on? Plain and simple, the creaks stem from wear and tear. Each step is made up of a few parts: the tread (the piece you walk on); two or more supports, called stringers (one on each side and sometimes one in the middle, under the step); and a riser (the panel that extends up from one tread to the next). Over time, constant usage—along with wood's natural expansion and contraction from changes in temperature and humidity—can cause nails and screws to move, and walking across the loose spots makes them creak, says home inspector Frank Lesh.
What to do Tighten up the creaky areas with reinforcements. "If you can access the underside of the stairs, you can glue shims between the treads and the stringers in the creaky spots," says Lesh. If you don't have access, you'll have to screw down from the tread into the stringer. Use a stud finder to locate the middle stringer, if that's where the creak is coming from. For screws that stay concealed, try the Squeeeeek No More floor-repair kit ($24, amazon.com).