There are several reasons why floors make cracking sounds:
Relative humidity: Ensure that the relative humidity in your house is neither too high nor too low. This may explain why your floor loosens and becomes noisy. A humidity rating between 37% and 45% is ideal.
Wrong type of subfloor: For nailed flooring, the subfloor must be made of plywood or OSB panels; the use of particleboard is not recommended.
Wrong subfloor thickness: The recommended panel thickness is ¾ inches (plywood or OSB) for joists spaced apart 19 inches or less, centre to centre. Spacing exceeding 19 inches or a greater span can result in deflection, leading to cracking sounds.
Board direction: Boards are installed in the same direction as the joists.
Structural weakness: The subfloor is not firmly anchored to the joists with flooring screws; there are gaps between the subfloor and the joists.
Lack of anchors: When boards are not anchored securely, they may move and lead to cracking sounds. Each board must have a minimum of two nails two inches from board ends, ideally spaced at eight-inch intervals in relation to the board length.