Some of the 3.8's experience cracked exhaust manifolds.. not big cracks. Usually what happens is you hear the tick when you start it cold, and it silences fairly quick. As the crack grows you realize it's an exhaust leak because the sound changes. Mine has a crack in the left one right now, it started with a tick and now sounds like a 454 with a bad donut, for about 3-4 minutes. This could be the sound your hearing.I have noticed a ticking sound coming from underneath my Jeep after being parked outside in the cold, but only temporarirly, on acceleration only. Not coming from the motor, but from underneath. Can't figure it out. Advice on what to check?