I have a 96 2 door blazer with a 4.3 automatic that seems to make a strange front end vibration noise when I hold down the brakes and shift into reverse. There is a loud "clunk!" noise while shifting and holding down the brake pedal. I checked the u-joints and the drive shaft has no play in it, so I suspect those are fine. Now the front end vibration feels like it's pulsating through the steering wheel and the brake pedal. It only does it in reverse at a complete stop while the brakes are applied. When I put it in drive the vibration goes away. Again this is NOT while I am moving. It's only at a complete stop when when the brakes are applied in reverse.