Driveshafts are made of steel and aluminium and contain U joints that permit the shaft to turn at angles. When driveshafts are manufactured, they are balanced by a weight welded on the sides. The signs of an imbalanced driveshaft are comparable to those of an out-of-balance tire. You can check the driveshaft yourself to see if it is imbalanced.
Chock your wheels to be certain the car is parked on a level surface. Make sure the parking brake is set.
Insert a floor jack under your car's lift point. Raise the car until you have enough room to access the driveshaft and install the jack stand underneath the vehicle.
Put on your safety glasses and crawl under the vehicle. Grab the driveshaft. Turn it to the left and right with your hand to check the U-joints. If there is excessive movement, the U-joints might need to be replaced.
Inspect the driveshaft for abnormalities. If it has dents, it might be imbalanced and in need of replacing.
Remove the jack and lower it to remove wheel chocks
Test-drive the vehicle to see if the driveshaft is balanced. If it is not, it will create a vibration in the seat and floor.