Trunk Lid problems of the 2000 Chevrolet Malibu

This complaint stems from the time I have had this car. A popping noise that comes from the rear of the vehicle from either both the trunk area and or suspension, a hollow sound not very loud though. It happens on uneven surfaces at very low speeds. I brought the car to the dealer four times and sometimes the sound or sounds are noticed but nothing is done,except for lubrication. Sometimes it is hard to duplicate and at other times it can. Also it never happens at highway speeds. Only slow speeds and on right or left turns. I hope that the engineers can discover it. The car is a 2000 Chevrolet Malibu. VIN 1g1nd52joy6211245. The car is still under warranty.