A cat's voice may become hoarse due to the following reasons:

1. Drinking less water or getting angry: This may cause the cat's voice to become hoarse. When a cat gets angry, inflammation of the cat's throat may occur, causing the voice to become hoarse.

2. Howling excessively or barking for too long: Cats may have a hoarse voice due to excessive use of their throat.

3. Foreign bodies in the throat: Cats may injure their throats when trying to swallow foreign bodies, causing a hoarse voice or even retching.

4. Throat infection or inflammation: A cat's throat infection or inflammation can also make the voice hoarse. This may be due to a viral or bacterial infection, such as calicivirus.

5. Tracheitis or respiratory diseases: Cat’s tracheitis or other respiratory diseases may also cause hoarseness, usually accompanied by coughing symptoms.

6. Cold: After a cat catches a cold, its throat may become inflamed and swollen, resulting in a change in voice. At this time, the cat needs to receive appropriate treatment, such as anti-inflammatory drugs to relieve symptoms.

If your cat has a hoarse voice that lasts for a long time or is accompanied by other symptoms, it is recommended to take the cat to the veterinarian for examination and treatment as soon as possible.