Secure Boards from Below (If Accessible)

If you have access to the floor from underneath (e.g., via a basement or crawl space), locate the creaking area. Have someone walk on the floor above to pinpoint the loose board(s) and joist(s). Apply construction adhesive between the subfloor and joist, and/or drive short wood screws up through the subfloor into the base of the floorboards (use screws short enough not to poke through the top surface). This tightens the connection.