Have an 05 STS N* RWD. I have a tapping noise coming from what sounds like the right side of the motor. It is more prominent above the back 2 cylinders. The sound is like tapping the shaft of a screwdriver on a wooden workbench. The noise tends to disappear at times. Can hear it under heavy acceleration and at idle. Especially noticeable at idle when standing by drivers door. The car has 86000 mi and I think it lacked WOT's by the first owner. I am the second owner. Hot or cold the noise is pretty constant. It disappears when accelerating in park in the driveway. Exhaust cams? :hmm: I got the car for $8000.00 and it is in nice shape.