Rodents use ultrasonic songs to claim territory and attract mates with high-pitched love songs. It has been discovered that mice and rats don’t use vibrating vocal folds in their larynx to make ultrasonic sounds but they do it in an unusually different way. Their singing method is similar to that of a jet engine. The rodents point a small air jet coming from the windpipe off the inside partition of the larynx. The mice and rats vocal pleats remain totally still during the making of the ultrasonic screech. Ultrasonic sound refers to anything above the frequencies of audible sound, and technically includes anything over 20,000 Hz. Rodents are the only known animal to create this ultrasound fabrication process. The only other machine to make this noise is when a jet airplane takes off or lands and specialized jets designed to rapidity cool electrical components and turbines.
https://www.linkedin.com/pulse/rats-mice-ultrasonic-love-songs-randy-bilesky?published=t
http://www.delta-optimist.com/opinion/blogs/blog-rats-and-mice-and-ultrasonic-love-songs-1.2362334