The reasons why a cat’s chest vibrates and makes a low motor sound:

1. The cat feels relaxed: The cat feels relaxed. If the cat has positive emotions such as being more comfortable, satisfied and happy, it will make this sound. This can usually be found when a cat is sleeping in, basking in the sun, or being petted by someone he likes.

2. Cat stress response: Cats will make this sound when they are unfamiliar with the surrounding environment or are fearful. Cats should use this sound to comfort themselves, hoping that their emotions will calm down as soon as possible.

3. Cat is sick: When a cat suffers from respiratory disease or heart disease, it will make this kind of motor sound. If the cat makes this kind of sound anytime and anywhere, the cat should be taken to Pet hospital for examination and treatment.