First, Dr. Anthony Pilny, DVM, who has assisted JoinRats in making several health-related videos currently on JoinRats, talks in a Howcast YouTube video about "normal rat sounds" and how to interpret them.

An important companion to "normal sounds", is the category of "abnormal sounds."  For pet rat lovers, this topic is critical, because almost all pet rats are born with an incurable bacterial disease, Mycoplasma pulmonis, which resides first in their respiratory systems and can cause early death. For this topic, please visit "Healthy Squeaks or Sick Squeaks, What Does Rat Respiratory Illness Sound Like?". 

The other videos below Dr. Pilny, are examples of normal rat squeaking.