Hi Robert,
Thanks for your question.
For a cat that is a standard domestic shorthair then 10 kilograms is a huge weight to be. Obviously there are some breeds of cats that are that big but definitely, obesity is something that can cause this. If he is obese that can cause the airways to become narrow, cause noisy breathing and snoring. Also, bearing in mind that an increased weight also increases the risk of arthritis, diabetes, skin disease, and fatty liver or hepatic lipidosis in cats as well. Therefore breathing noises can be an indicator that there is a problem with obesity, but there are a lot of other risks as well.
If your cat is brachycephalic so these would be the squashed, short-nosed breeds like a Persian, Himalayan or a Burmese. These brachycephalic cats have as many problems as do the brachycephalic dogs as they can have narrow airways, long soft palettes, and the throat and larynx can have abnormalities meaning that they create the kind of noise you’re describing which is again a symptom of the problem with the breathing and the narrow airway. If none of these are a problem and he is otherwise healthy as described, then it’s unlikely to be a problem. Keep an eye out for the breathing changes and I would suggest that you take a video of your cat while he’s snoring, while he’s grunting just to show your vet the next time that you visit because a video is a really powerful tool that we have to show changes that can be quite difficult to describe.
I hope this helps.
Dr. Alex Avery