I have 1600Km on a brand new AT4 , I find it is way quieter than the Eco-diesel I had for the previous 5 years. The only diff in noise in the cab I notice comes from the Duratrak tires. Had KO2s on the RAM but the Goodyears are way louder on the highway. I cannot hear the engine at all over the sound of the tires .Slight volume adjust gets rid of the tire whine. The only other noise I notice comes from the fuel pump in the tank, it is much louder than the Ram. Loud enough that I may take it to the dealer to see if that is normal. On the whole very impressed with the Duramax , average 10l/100km on mostly highway driving at around 120kmh.