The answer to 'why is my flea scratching sounds' is that your pet likely has a flea infestation. Fleas are small, wingless insects that feed on the blood of animals, including pets and humans. When fleas infest a pet, the itching and scratching is a common symptom as the pet tries to relieve the irritation caused by the fleas.
Flea infestations can happen for a variety of reasons, such as bringing home a new pet with fleas, exposure to fleas in the yard or at a pet-friendly location, or even just a breakdown in your regular flea prevention routine. The scratching sound you're hearing is your pet trying to relieve the intense itching and irritation caused by the fleas.