Here we go again
1. Its not "Wastegate flutter" The noise you hear, is the blade of the turbo shuddering with the boost pressure trying to escape when the butterfly valve is closed (throttle)
2. You wont get it from mfi, cos the metering head muffles the noise.
3. If you really want it, you need to go on to efi or an afermarket managment.
Rant over.