Here's a qoute from Paul Tan's website...
Chevrolet introduces 2nd-gen MY14 Duramax diesels
"Also redesigned are the cylinder head and cylinder block, both lighter but with increased cooling efficiency. Finally,
a balancer shaft has been added to reduce vibration/noise and promote smoother operation. The
units also feature a new engine control module, featuring newly-developed software, for quicker response and added accuracy."
It is very clear that the Duramax2 (2014 models -trailblazers/colorados) has a number of enhancements that contribute to its "quiteness" compared with the Duramax1 (2013 model and below). I took a peek on the engine bay of 2014 colorado and found it is now using a new engine control module different than the previous models. Note that NVH levels are a direct influence of engine design and techniques in fuel injection (multi injection) strategy. this requires advanced electronics hardware and software technology.