A pilot was flying alone at 30,000 feet altitude when he heard a rattling noise in the plane. He immediately depressurized the plane (let the air out) and allowed the pressure in the plane to drop to that of the outside atmosphere. A sudden depressurization is generally considered very dangerous, so why did he do this?
HINT 1: He did this for his own safety.
HINT 2:The rattle alerted him to a problem which might become dangerous.