So I have an EGR delete, head studs and gaskets replaced, along with a Garrett Powermax, everything was done last May so everything has less than 20k miles on it. This is the 3rd time I got to tow with it since it has been done and was on the return leg of a 700 mile trip, and this noise started. Seems to vary with throttle, still does it with radio and heater off (did this first as I was cruising down the Interstate), and it is so loud that it is hard to pinpoint it's exact location.
Let's play name that noise: