A cat's breathing is normally so quiet that you can barely see or react to it. A cat with normal breathing breathes quietly and no sound should be heard from the nose, throat or airways.
A normal breathing rate in a resting cat is about 20-30/ beats per minute. If your cat's respiratory rate is higher than this, the cat's respiratory rate is elevated and a veterinarian should be contacted. Even if breathing is felt to be more shallow and faster (elevated rate), a veterinarian should be contacted immediately.
If you notice that your cat is breathing more labored, you should also take this as a warning that something is wrong. Cats with labored breathing often breathe using their stomach, which moves when the cat breathes. This is a very acute condition and is very distressing and painful for the cat. If you notice this, you should contact a vet immediately to get your cat help. Sometimes it is also possible to see that the cat is trying to position itself in such a way to get air more easily, in which case you should also contact a vet.