Like humans, dogs make all sorts of noises while sleeping, such as burping, passing gas, barking, whining and growling. Sucking noises are not as common, but some dogs do make them regularly. These noises may be the result of an unusual habit, or they could indicate a serious health problem.
Suckling
Most dogs quit making suckling movements in their sleep shortly after being weaned. Some keep this habit throughout their lives, however, and will make sucking and slurping noises as if they were nursing nearly every time they rest. Dogs who do this will sometimes actually suck on an object, such as a toy or blanket, and become distressed when the object is not available. There are no adverse health consequences to this habit.
Inflammation
Swelling in the nose and throat can cause your dog to snore as well as make unusual noises in his sleep, such as sucking and slurping. Swelling can be caused by a number of health problems, including allergies, an upper respiratory infection, tumors, lesions or coughing. If your dog suddenly starts making unusual noises while sleeping, has difficulty breathing or you suspect that tissue in his nose or throat is swollen, contact your veterinarian.
Brachycephalic Skull
Dogs with short noses and flat, wide faces, such as boxers, bulldogs, pugs and Boston terriers, are brachycephalic, which refers to the shape of their skull. These flat facial features frequently result in a soft palate that is too long, narrowed nostrils and voice box abnormalities that cause unusual breathing sounds, both when your dog is awake and when he's asleep. Most often this means snorts and snoring, but can also include sucking and rattling sounds as he takes deep breaths. Although this is normal for brachycephalic breeds, there are treatments for dogs with severe problems, such as surgery to widen the nasal passages. Check with your veterinarian to learn what is considered normal for your individual dog, or whether he needs treatment.
Other Causes
Anything that causes your dog to breathe in a different manner than usual can cause him to make strange noises in his sleep. This includes laryngeal paralysis, heart failure, excess tissue in the throat and mouth, foreign objects, edema and a discharge of fluid, such as pus or blood. These conditions are not considered normal and should be checked by a veterinarian.