It seems like around 2003 or so the diesels all got A LOT quieter. I remember once I stopped to take pictures by the road and a guy in an older Cummins pulled up to ask directions and I was standing at his window. He had to turn his engine off so we could hear each other.... that things was NOISY.
My 06 Duramax is louder than a gas engine for sure but really not all that much. I rarely have to turn it off in a drive-thru. This is my first diesel and honestly one of the things that turned me off from them for years was the noise.