Inside the wheel hubs are either roller or ball bearings that carry the vehicle's weight. On RWD vehicles with solid axles, the rear wheel bearings are mounted on the axles. The front wheel bearings on older rear-wheel drive cars and trucks usually require "repacking" (regreasing) every two years or 24,000 miles. The wheel bearings on most newer vehicles are sealed and do not require any maintenance. A bad wheel bearing will typically make grinding, whining or squealing noises, and you can often feel the looseness or roughness if you raise the suspension and rotate the wheel by hand. Worn wheel bearings should be replaced, because failure may cause the wheel to come off the vehicle.