what noise? its just the sound of an unsilenced exhaust at high rpm.

if you hear a external wastegate venting at low rpm you will see it just sounds like a POS.

its hard to tell, but a lot of the whistle from a turbo car is actually out the exhaust, so that again is part of the screamer noise, jus unsilenced.

BTW, external or internal wastegate, even if they plumbed back into the main system you can tell when the wastegate opens if your exhaust is loud enough.
on my cossie you could tell the exact time it hit full boost and the wastegate opened as the noise would get a lot louder as the turbine was no longer silencing it...