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.....

 No that is not normal. You need to get your cat to the vet as soon as you can.