Since you are having trouble isolating the sound, they have dignostic stethescope and like Steve says, spray grease (I use good ol' WD40) and spray around the exhaust system joint and manifold locations. Remember, since you do not have rubber mounting, you may want to check for loose hardware. On my '04 (it HAS rubber motor mounts and links, but I still have seen vibrations loosen mounting hardware, even the baffles inside my pipes, with just a 1/4 turn of tightning. Also the chain tension is manually adjusted, so you may need to view a service manual to help map your strategy.