2. Differential gear or bearing: A worn or damaged differential gear or differential bearing can also cause humming noise from under the rear seat of the car.
3. Worn wheel bearing: This can cause a humming noise regardless of the speed of the vehicle. Check the wheel bearings by putting the car on stands, starting it, putting it in neutral, and spinning the wheels by hand. A bad wheel bearing will feel rough or notchy.
4. Loose or damaged exhaust system: A loose or damaged exhaust system, especially near the rear of the car can produce a humming noise when the car is in motion.
5. Low tire pressure: Low tire pressure can cause a humming or growling noise, especially at higher speeds.
6. Wind noise: Wind noise can sometimes be mistaken for a humming sound, especially at high speeds.
7. Faulty electrical component: In rare cases, a faulty electrical component, such as a malfunctioning alternator, can produce a humming noise.
