A cat suddenly developing a hoarse voice may have the following causes:

Upper respiratory tract infection: such as a cold, which can cause a sore throat.
Allergy: Allergic to factors such as food and environment.
Excessive shouting can lead to vocal cord fatigue.
Foreign objects in the throat: such as hair, food, etc.
Environmental changes: Stress or anxiety may affect the voice.
External injury: Throat injury.
Diseases or infections: such as feline infectious peritonitis.
If your cat's vocal changes persist or are accompanied by other unusual symptoms such as coughing, difficulty breathing, or loss of appetite, it is recommended to take it to a veterinarian for examination and diagnosis as soon as possible. The veterinarian can determine the specific cause through examination and provide appropriate treatment recommendations. At the same time, ensure your cat's living environment is clean and provides plenty of water and nutritious food.