Wheel bearing are a tough set of steel balls that allow your wheels to spin effortlessly and with less friction. They can last over 100,000 miles, but with all parts they will eventually wear down, especially due to water and heat. Your first sign that your wheel bearing are beginning to fail will be a noise. This noise will progressively get louder the faster you accelerate. You may notice some shaking too. On a more serious note, the wheel bearings are what keeps your wheels attached to your vehicle, so it is extremely important that you come in for a replacement as soon as possible.