When your house creaks and groans at night, it doesn't mean it's haunted.

"What you hear is the wood contracting and expanding as it picks up and gives off moisture," says wood specialist Julian Beckwith in Family Circle magazine.

The substance that gives wood its main structure - cellulose - attracts water from the air. Old buildings often make more noise than newer ones that have modern air conditioning and heating to keep the humidity constant.

"Such creaks are harmless," says Beckwith, adding, "I think they give a house personality."