I thought #4 was the tensioner and #9 was the guide with #6 being the idler. Whatever they are called it is the pulley in #9 position that is making the loud chattering noise and seems to be vibrating/wobbling. I will take tear the serpentine down this weekend and see if things need to be tightened but I would like to replace as many of the pulleys as I can. They all seem to prone to malfunction. Anyone with any info would be appreciated.