I have a 2007 Jeep Grand Cherokee Laredo 4.7L and it has a clinking sound that comes and goes. At higher speeds 35+, it is accompanied by a vibration. If there is a vibration at lower speeds, it isn't noticeable. It comes and goes and can be a few days to a month apart. It sounds like it is coming from the center of the vehicle below the front seats. Below is a link to a video that I recorded while the sound was happening.