The ecodiesel is definitely without any doubt, quieter than the Hemi. My neighbor and I compared his stock off the shelf 2016 hemi my Eco, and it wasn't even a contest. They are almost dead equal in decibels (measured with the iPhone app) on the outside while standing 5' in front of the truck They sound very different, but same decibels. Inside the truck, the Eco blew the Hemi away, much to the shock of both of us. I don't recall the exact numbers but it was something like 10% quieter at idle, and closer to 20% quieter when running 30mph.
First off, they purposely make the Hemi louder so it sounds "cool". This is especially evident when running 30mph +. Secondly, I think they might have added more sound deadening on the eco, but that is just a guess ?
I'm just seeing this...but then again, I didn't have my ED until Jan of this year.
Engine noise between the ED and 5.7? Wow...that's a hard one to describe. First off, I lived daily with a 5.7 2014 for a few weeks shy of 4 years...so I know that truck well. As far as noise? I'll have to break it down:
Cold idle:
-The 5.7 exhaust is loud when cold. Morning start ups, the exhaust is pretty stout, almost as if it had an aftermarket muffler on it.
-The ED cackles like a cement mixer full of gravel when cold, exhaust noise is nonexistent but the engine is typical diesel loud.
Warm idle:
-The 5.7 is really muted when warm at idle...really low rumble
-The ED has that faint diesel cackle when sitting idling.
Cold/in town driving:
-The 5.7 made quite a bit of cab noise with my '14. It was never intrusive, but it was notable at all times.
-The cackle gravel of the ED will continue until it is warm.
Warm-in town driving:
-The 5.7 is the same warm as it is cold.
-The ED cackle goes away 80%, the slight woosh/hiss of the turbo can then be heard. The blow off is slightly notable
Warm highway driving:
-The 5.7 is pretty notable on the highway. Nothing annoying in the slightest, but it can be heard.
-The ED is nearly silent...almost zero engine noise (which is crazy).