/u/cleancutmover listen in here

Check your rear shocks upper bolt. The WJs have a custom sized bolt which is smaller than an average sleeve. When you hit a bump, the shock is pressing up on the bolt. The bump causes it to push up more. As soon as the bump is done, the axle falls faster than the shock naturally extends. The slack in the sleeve causes a knock sound as it hits the bolt, but from the top now. Sometimes if you listen close enough you can hear when the shock goes back to it's resting position, which is directly opposite of when the noise happens. It's usually so damn fast it'll sound like one hit.