The planes you are noticing are all below the 10,000 ft level (i.e., on approach or takeoff) and are required to fly no faster than 250 knots. No supersonic ai

The planes you are noticing are all below the 10,000 ft level (i.e., on approach or takeoff) and are required to fly no faster than 250 knots. No supersonic aircraft will be flying supersonic on approach or at low altitude. If their engines are noisy they will be louder for the same amount of time as others.