I honestly think its coming from the rear end. The pitch doesn't change with gear selection or RPM. Very slight increase in volume under load. Its still present when coasting. Only changes pitch with speed.
I got a pretty good video of the noise, was going to upload it unlisted to YouTube and let you guys hear it, to see if its the same thing.
What parts are the same between the 150 and the Raptors? What could this be coming from? It sounds like my old 3.5 with an exhaust, but definitely isn't turbo whistle.