I have two 2000 Explorer XLT both have the SOHC V6. They both make the same noise when first started (cold start). It lasts only a second or two at most. It is a noise that resembles a diesel starting. I have always thought it was normal for the 4.0 SOHC. I don't think I've ever been around one that sounded any different. I have always thought it was tappet noise until the lifters were pumped up. It has hydraulic lifters, right? I could be ignorant and happy believing this is normal. One has 115K miles, the other 83K. The 83K motor has a new noise that got me reading some frightening threads here. On two occasions I have started the engine (warm starts) and been confronted with a sharp tapping/rattle sound that does not go away until the engine is shut off. It doesn't happen every time. I have not had it happen on a cold start yet. It is a slower rattle than the start-up clatter I described above. It sounds like it could be one bad hydraulic lifter. But in reading through some posts here, I fear it could be timing chain related. Can anyone confirm the normality of the cold start-up noise? Has anyone experienced the intermittent new noise? Would a broken plastic chain guide bouncing around under the timing cover make this kind of noise? 83K seems like short life for a hydraulic lifter, if that is the cause. This motor has had all scheduled maintenance.