there are six bolts on each exhaust manifold... if they are loose you have a nasty exhaust leak and it will make a ticking noise (makes it kinda sound like a lawnmower) tighten the bolts when the motor is cold.. i thought of something.. i had some spark plug problem once.. it ticked just like rod knock or valve tapping or an exhaust leak.. it got very bad one day and i took it to the shop.. ended up being something with the spark plug... just a suggestion if you havent checked those in a while...