Carry the car up and support it safely on stands. Crawl below the car, look at its drive shaft to see any dents in the tube or a crack visible on it. Any presence of these requires one to replace the entire drive shaft. Look for oil leaks at the front and rear end of the drive shafts. If there is leaking around where the driveshaft enters the transmission, then this means that there is an issue with the rear seal of the transmission; if there is leaking around where the driveshaft connects to differential; this may mean that your pinion seal is defective while if at all there is leaking around entrances into transfer case (AWD models) - your transfer cases' seals could be faulty. In addition to that, while under raise an assistant turn back wheel so that it would make a rotating motion of driveshaft. At this point ensure universal joints are not functioning properly by checking their free movement without making sound or being loose. Also in case a drive shaft does not move, you can test how universal joints are working by holding hands on either side of each coupling and twisting it cautiously. If it has just a little play on whichever side, then most likely it needs changing. Additionally, lifting upwards at any stage might reveal activity within them as well. Lastly, ensure that you have tightened up all your bolts which hold your drive shaft on both ends.