The most likely cause of stomach noises when a dog will not eat is gastrointestinal upset. The dog may have picked up a mild stomach virus or bacteria, or it has eaten something that did not agree with it.
Most dog's stomachs make gurgling noises due to excess gas in the intestines. This can occur when the dog hasn't eaten in a while, which allows the gas room to expand and move through the intestines more easily. If the dog is not hungry with these symptoms, it may still have gas from partially undigested foods. Another likely scenario is that the dog ate something that upset its stomach. The dog may have also contracted a mild stomach virus or bacteria.
If the dog has no other symptoms or only some mild lethargy, it may be appropriate to wait out the problem. Make sure that soft, easily digestible food is available, like rice or boiled chicken, along with plenty of water. Take the dog's temperature to ensure it does not have a fever. A dog's normal body temperature should be 101.5 degrees Fahrenheit. If the dog will drink, a small amount of antacid, less than one tablet, crushed in water may help soothe an upset stomach.
If it is some gas, the dog should pass it in a few hours. If it is an upset stomach, virus, or bacteria, the dog may be sick for a few days. However, if the dog does not take food or water within 24 hours, take it straight to the veterinarian. Dehydration can quickly occur if the dog is not taking water.