The driveshafts of your vehicle are turned by the gearbox, and connected to the wheel hub to turn the wheels. The inner and outer ends are fitted with joints, which are packed with grease and covered by a rubber boot. It's the rubber boots which cause most driveshaft issues as they get damaged by debris thrown up under the vehicle. When they are damaged they release the grease and let in dirt and grit which grinds between the bearings.

Regular inspection and replacement of damaged boots is necessary to avoid the large expense of replacing a faulty driveshaft on your vehicle.