Driveline Noise
 

I have a 1981 280E with about 67,000 miles that I just bought.

There is a flopping type sound in the driveline when the car is coasting, neither accelerating or decelerating. The sound disappears as soon as brake or gas is applied. I changed the front disk which was definitely bad. The rear one seems ok.

Do you all think this is most likely a rear flex disk problem? or am I overlooking something? Thanks a ton for the answers.