Yeah mine happened after going to a turbo back 3" with Hi Flow as well. I'm pretty sure mine is the same issue as yours Tony and it's either coming out the shaft or leaking past the wastegate.

Woja replacing the wastegate would require pulling apart your turbo and I'm not sure what the success rate would be or how feasible. Just drive around for a while, you might find knowing that it's harmless makes it less annoying.

It's on my long to do list to find a real solution to this but I'll probably just end up putting a VF34 turbo on there in the future to make it go away.