A rear-drive or 4-wheel drive car has at least one propeller shaft to the rear wheels. Some 4WD systems have propshafts to both axles. Hold the shaft on each side of a universal joint and try to twist it in both directions. If there's free play, the joint is worn and should be replaced. Also, carefully try to turn the propshaft back and forth, where it enters the transmission or transfer case, and if there's free play between the propshaft and its mating shaft, the end section of the propshaft (called the slip yoke) may be worn and in need of replacement. If a propshaft is very long, it may be supported in the middle by a center bearing assembly. Inspect this for a loose mount and turn the propshaft while you feel the bearing assembly for any roughness.

Even if everything is tight , remove any mud or debris packed into the universal joints, and if there's a U-joint grease fitting, lubricate it. Although original equipment shafts on most recent 2wd and 4wd vehicles have sealed and packed joints, OEM joints for most older 4wd systems have grease fittings. This is also true for many replacement U-joints.