Im new to the gas side always been on the diesel discussion.
I traded a vehicle for this very clean 87 560sel with 260k miles and need some help with a vibration. It's a very fast vibration and is louder when I decelerate. (vibration isn't really loud and can barely feel it). The vibration starts at 55.
My Cummings truck had a gear bender box that went out and it almost sounds like that but the gear box was much worse.

When I do 70 and put it in neutural the vibration is still there but quieter.
Vibration there when accelerating and slightly louder when you decelerate. Vibration stays the same when you cruise.

Is this the middle drive Shaft bearing?

Thanks for your help.