I was wondering if, like on some other turbo diesels, the LLY had a turbo silencer that could be removed. If so, how?

it does have something to that effect, a turbo muffler IIRC... you can remove it and plug the cap with something else i would assume but not sure if you would get anything out of it or not as im not sure exactly what it does - maybe someone else can help out with that ?? I know that the True Flow Air Intake System for the LLY comes with a cap, and the directions say to remove the baffle, and replace with the cap. I tested along time ago with it on and off, and i wasnt convinced that it made much difference, not sure though exactly

Did it increase turbo whistle?

If you are talking about how the Cummins has a silencer ring. The Duramax does not have a removable silencer ring in the turbo you can take out. I guess you can pay $200 for an air intake.