BMW Repair: vibration at 50 mph, bmw 520i, shaft bearing

Question
BMW 520i 1992 24v 5 sp, auto, a vibration occurs when in 5th gear, at 5omph, it still vibrates when speed increases, stops when lifting off the throttle,i thought maybe bad tyre balance, and had them done, no difference,i,m thinking prop shaft bearing, has it got a centre bearing ( the rubber type)?, look foreward to hearing from you.thanks john.

Answer
Check the driveline for balance, have you had work done on it ever?  it's likely the driveshaft was installed without being lined up or some of the balancing weights fell off or were damaged.  Other possibilites include as you said the center bearing and or engine and trannie mounts.
-cheers