Pretty sure i get the same thing (Same turbo as you) .. Only when i'm in 4th and plant it .. Get the fluttery sound during spool then it disappears. I am running a bell-mouth dump dump though, not a flat plate.

I think this was brought up before, I was under the impression it was the motor not being able to "ingest" the amount of air the turbo was supplying at that given point, may be able to be tuned out to some extent but the fix would be bigger cams, porting the heads etc.

My 2cents.

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Should have bought an STI