Those rubber bushings allow for quite a bit of movement especially if they are worn out or the rubber is busted loose from metal mounting parts.
Keep in mind, the two rubber bushings on the ends of the boomerang are bolted to the body right under the back seat, so any movement of the boomerang that is not absorbed by the rubber bushings in the boomerang and allows for excess movement will make a clunking sound that is transmitted into the body where you can hear it.
On mine, sometimes if I take off from a dead stop and let of the go pedal just enough to take most of the load off the rear axle, sort of like freewheeling, and the transmission changes up to a next higher gear while it is in this condition, I will get (hear) a loud CLUNK from under rear end. My boomerang has been replaced with a Mopar unit and is fairly new, so I just ignore the sound and mark it up to design of the vehicle.
And I have checked the lower control arms and bushings and they are all in good shape!
Before I replaced the boomerang right after I purchased the Jeep, there was lots of noise coming from under the rear seat area anytime I rode over a bump in the road. I live on a dirt road with lots of bumps, so I get to test it every time I drive it!!! The rubber bushings on the OEM boomerang were worn slap out, busted, and allowing the metal boomerang to contact the flanges of the body where it mounts. I could see the shiny metal where the two had been making contact....
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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