Final answer:
The possible cause of the strange squeaking sound from Harriet's car could be that the brakes need to be replaced.
Step-by-step explanation:
The possible cause of the strange squeaking sound from Harriet's car could be that the brakes need to be replaced. When brakes wear down, they can produce a high-pitched squeaking sound as a result of the brake pads rubbing against the rotors. This indicates that the brake pads are worn and need to be replaced.