you usually get like a whoooo noise at idle because BB turbos spin faster at idle than plain bearing turbos (ie td04). You'll notice the same noise, when you turn off the engine as a BB turbo will keep spinning for a little while after you switch off the engine.
You really need a retune though with a new turbo. GC8s can usually tolerate small turbo changes without too much trouble. Regardless though, your never going to get the most out of the new parts unless you get a retune or upgrade
ECU (assuming you still have OEM
ECU).
What model WRX do you actually have?