1990 760 Turbo: braking from 50-60 mph results in a vibration felt from the rear of the car. It's not noticable on light braking, but appears when some heavier pressure is applied to the brake peddle. I assumed that I was dealing with a warped rotor, but the gauge says less than .001" runout. The caliper slides (Girling) aren't stuck, and there's no "obvious" bushing problem. Shaking the suspension parts with the car on jacks results only in sore wrists. There is a muted "flub, flub, flub..." when the axle is rotated, with the sound, and very slight vibration, coming from the differential (not a limited slip variety). Shaking the exhaust pipe, just ahead of the axle, results in a slight knocking sound. The tires are virtually new Bridgestones. Again, the vibration is felt only when braking, and only becomes obvious at freeway speeds. Any help in diagnosing, or pointing me in a direction, would be greatly appreciated. Thanks!!