I too have been suffering with a clunky check strap on a rear door which has been improved with a smear of grease. The tailgate has a loud creak when opening. Engine oil on the hinges, the gas strut ball and socket joints and a smear on the sliding connecting rod has done little to improve it. I have not had a chance to investigate further but I have a feeling the gas struts are to blame. Maybe take them off and put a smear of silicone grease in the locating sockets will help.