Mine does this, but i know its turbo play that causes mine. I have a rebuilt unit here to put on, just havnt had time yet.
If you remove the boost pipe and spin the turbo,it should spin freely with no real resistance, it also should have almost no detectable play in the shaft.
My bet is you now have some endfloat and it sucks a bit of oil into the turbo itself. Due to the small amount it burns off un noticably