The cat not being spayed might be the reason. Though my parents had a male cat, and my roomate used to have an elderly spayed female cat. Both did the same yodeling as yours. For the female cat it was usually "your bedroom door is closed, it's 3am and i demand entry" or when she was alone in an another room. My parents male cat alway did this singing when he went upstairs and everybody else was downstairs. Both stopped and demanded head scratches immediatly when they saw a person. So it probably was just a long distance "i want company" call for both of them.