If you begin to notice that your stairs are squeaky or loose as you walk up or down them, inspect them and make needed repairs. Stairs are often repaired with wedges that are installed along the stringers (side stair supports) at the joint between the stair riser and stair tread. Over time the wedges can become loose due to repeated use. Repair these wedges by removing them and refastening them in place. Using screws will help prevent the wedges from shifting over time.
Identify the shifted stair wedges on the underside of the squeaky stairs. Look for wedges that have a space between the tread and riser. These are the problem wedges that are causing the stairs to be noisy.
Slide a flat bar under the wedge and carefully pry it off from the stair stringer by pulling the bar outward.
Pull the finish nails out of the wedges with diagonal pliers. Fit the wedges tightly against the stringer so the top edge is tight against the tread and the back side is tightly against the riser.
Drive one wood screw through each corner of the wedges into the stringer using a screw gun to secure them in place.
Inspect noisy stairs as soon as possible to prevent the loose treads from becoming damaged.
Wear eye protection.