No that is not normal. You need to get your cat to the vet as soon as you can.
Pallio, this is certainly not normal. Most cats breathe without any sort of a hiss or sound. I suggest that you should take your pet to a well-qualified vet and seek his consultancy.
Seems as though your cat may have a respitory problem and should be seen by a vet asap ..it is most definitely not normal for a cat to breathe loudly.....