A rat alternates between chattering, squeaking and hissing. The chattering noise is produced when a rat grinds his teeth together and can indicate both stress and relaxation, while squeaking and hissing convey fear, pain or alarm. Chattering is also known as bruxing.
A rat can squeak when happy, but these vocalizations are high-pitched and inaudible to the human ear.
Rats can emit ultrasonic vocalizations. Different frequencies are associated with different emotions or activities. A squeak at 20 kilohertz signifies distress, while the same noise at 50 kilohertz indicates happiness. Sex, aggression and contact calls are all produced at different frequencies.
However, a rat's squeaks can sometimes be confused with the abnormal breathing sounds that he makes when ill. Short, abrupt squeaks are a pet rat's way of communicating with a human, but when the sound is synchronized with the rhythm of a rat's breathing, he is most likely suffering from a respiratory disease. In general, a healthy rat does not make much noise.
Rats combine noise and smell to communicate with each other. A rat emits pheromones to warn others of danger or mark his territory, and sometimes to attract or interact with the opposite sex. In contrast to their highly developed sense of smell and hearing, rats have poor vision and avoid the light.