If you begin to hear a howling or a whining noise while your vehicle is turning, it is about time to change your differential gear fluid. You see, all the wheels on your vehicle travel at different speeds as well as distance. Your front and rear wheels also travel at different distances from the other. It is recommended that you change your fluid between 30,000 and 60,000 miles. When the fluid gets low or dirty it will lead to accelerated wear, and potentially cause, permanent damage to the gear.