Over the past couple of weeks I've had a lot of vibration/rattling coming from the rear of the car at 70mph+. From all of the threads I've read, it sounds like it could be a u-joint going out on the driveshaft. I jacked the car up with a buddy the other day who knows a lot more about cars than I and we tried turning the driveshaft with our hands. It was turning maybe 1/4". He said that's not as much play as he expected but he doesn't know a ton about these cars either.

Can anyone confirm whether it's normal for the driveshaft to turn that much by hand or could that be a sign of a failing u-joint?

Any help is appreciated!

UPDATE:
I went ahead and just took the car in to get it diagnosed. Turns out that both my rear brake calipers were seized and had caused both of the rotors to warp pretty bad.

 

Thanks for taking the time to update the post with the cause.