In 99% of cases, the creaking is caused by nails that have come loose in the wood. In many homes, especially older apartment buildings, the hardwood floor is nailed directly to the subfloor. If the subfloor is uneven and/or there are large gaps between the boards, the parquet pieces begin to wobble, causing the nails to loosen and resulting in the squeaking.
Due to the settling of the gravel fill beneath the subfloor, the boards lose their support, so they begin to spring under a person’s weight, which also leads to the nails loosening. In very rare cases, when the subfloor insulation is not perfect and a small amount of moisture rising from below “feeds” the parquet, the expansion causes the parquet planks to press so tightly against each other that they may emit a crackling or creaking sound.
