I have a 2003 TJ and just did some preventative work replacing water pump, hoses, inlet tube, rad cap, thermostat, antifreeze. Came out nice, so while I was there, I decided to replace the pair of PVC valves (one metered, one open) because the valve cover seems to be getting more oily, quicker, than it used to. That finished, my heater air control selector switch wouldn't work...found the vacuum line that I had knocked off, replaced, works fine.
What I have now is a rattle, engine speed linked, at higher rpms, (very much like the sound of engine knock at lugging speeds) that seems linked to higher rpm NOT load. I first thought: another vacuum line I knocked off...but I can't find anything off, and the motor runs excellently. another note: for the first few minutes on a cold engine, no knock at all. -as it warms up, then that deathly rattle starts....not real noisy like lugging, but there. Thoughts??