149K on my 02 intrepid. When I first start up the engine I get a chatter noise. Sounds like valve rattle. After 2-4 seconds the sound goes away. When I drive the car the engine sounds like it is grunting. I have no loss of power and after about a minute or so everything is normal. My oil and filter is changed every 5K and I take very good care of my car. I burn nor leak any oil. I live in so. calif. and drive in no snow nor severe cold weather but in summer the weather gets very hot. I have noticed this noise is becoming increasingly louder. I'm using Castrol High Mileage 20-50 oil at every oil change now. I haven't cleaned the injectors nor the throttle body. Perhaps that is the problem. What do you think?? This old back yard mechanic needs help..Thanks

 

My 3.5 in my 2000 R/T does this especially in the colder weather. Its normal for these engines....you might want to ditch the heavy weight oil tho to aid in better cold starts.