On some models, a rubber coupling is installed between the driveshaft and transmission instead of a universal joint. Wear in the universal joints is characterized by vibration in the transmission, noise during acceleration, and metallic squeaking and grating sounds as the bearings disintegrate. The joints can be checked with the driveshaft still installed, noting that it will be necessary to remove the exhaust system and heat shields to gain access. If the driveshaft is in position, try to turn it while holding the transmission or differential flange; free play between the driveshaft and the front or rear flanges indicates excessive wear. If the driveshaft is already removed, check the universal joints by holding the shaft in one hand and turning the yoke or flange with the other; excessive axial movement means the driveshaft should be replaced. At the time of writing, no spare parts were available for replacing the universal joints, so if any joint shows signs of damage or wear, the complete driveshaft assembly must be replaced. Consult your BMW dealer for the latest information on parts availability. If replacement of the driveshaft is necessary, it may be worthwhile to seek the advice of a driveline specialist, who may be able to repair the original shaft assembly or supply a reconditioned shaft on exchange.