Well after reading all 5 pages of this stuff, I am left wondering. I am looking at buying an 05 Navigator. Seems like a good deal, but the ticking is pretty bad. Seller/owner says it has an exhaust leak and a $108 manifold is the fix. I did not notice any exhaust leak, but he said yeh all the 5.4s like this make the valve train clattering. I think once I had my head burried near the timing chains he knew I wasn't listening for exhaust. I have a 98 Expedition that had manifold studs fail on and thought it may have been similar. But now it sounds like the common ticky...He said he runs 5-20 Castrol Syntech. Another thread here said something about Mobil One versus conventional 5-20. Synthetic "too" slippery? I have not heard anyone state failures or big trouble from the noise. I caught a couple about pops and figured back fires from the phasers maybe. Any advice PRIOR to my pulling the trigger...or making an offer? Aprreciate it!