I am telling you what it is based on my understanding of turbochargers and my experiences with turbocharged cars. New turbos with this sound is install error or incorrect remans. Overspeed wears the bearings out and this is the result. You don't have to believe me, but that is what it is. For people who are all stock with this sound, are you the original owner? How many miles?
This isn't a new problem, these aren't new turbos (this family of turbos has been used in different forms for ~20 years), doing a minimum amount of research will get you to the same conclusion. Or just ask Tony what he thinks causes the problem and he will tell you the same thing.