So called diesel sound like is the nature of this Beast. I wouldn't worry about it , disappears after warm up. However personally I'm strongly against using any oil additives to quiet it down. Many of the additives can change viscosity of the oil and that may cause a problem with VVT. As long as you use good quality full synthetic 5 W 30 oil like mobile one you should be fine. It does have outstanding lubrication during a cold start. Don't forget that most of the engine's wear occurs during a startup , so quick oil flow is very important. Some people putting a 10 W 30 oil to quiet the noise but not me. I prefer to stick with 5w 30 good quality synthetic oil for better fuel economy , less wear on the engine and quickly warm up. That's just my five cents
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