How to fix a squeaky staircase

With the housed-stringer type, there are typically no fasteners going through the surface of the treads. You need to get access from underneath the stringers, which may mean pulling down a drywalled or plastered ceiling in a staircase below. With this type of stair construction, the treads and risers are secured with wedges. Re-glue and reinstall any broken or loose wedges, tapping them into place to secure the treads. If necessary, stiffen the stairs by using construction adhesive and screws to add extra blocking where treads and risers meet.