So, just an update, my 2017 6.2L does the same thing. I heard it as the wiff started it just now and I was outside. Definitely leaning towards high pressure pump. It growled for a split second after startup. Kind of reminds me of the 3800 engines in the W body cars when they started. Back then I think it was a timing change that made the growl - timing retarded for cranking and then increased with initial engine rpm.........put 100's of thousands-za on those cars w/o any issues whatsoever.
I'm gonna run it. At least with 130k I think I'm past the new main bearing failures....LOL