From what I have seen it will be turbos, Theres no need to be oil if seal are leaking it can burn off... I have same problem and also got wastegate rattle, MHD wastegate fix set to 80% minimal lag. fixed it partially, so it has something to do with waste gates not fully closing/opening, don't know why it happens.
But this is my best theory and also lot of people fixed this when they replaced turbos, I will be replacing mine fot viv 19t V4 and index 12 injectors (bank 2 is leaking)
