The vocalizations during estrus: Cats make special vocalizations during estrus to attract mates. Sometimes, due to the distinctive tone, these vocalizations sound like a child crying.
Physiological or psychological reasons: Cats may vocalize abnormally due to physical discomfort or pain, or due to loneliness, anxiety, or seeking attention.

Nocturnal instinct: Cats are nocturnal animals, active at night to hunt. This innate habit may cause cats to be more active at night, thus making more noise.
Seeking or craving food: Cats may express their need for food or water by making loud, sharp meows.