Why's the check engine light on?

Have you tried to have someone rev the engine while you try to pin point? You may consider a mechanical stethoscope and touching things around see where's coming from.

It's hard to diagnose noises the internet, but a couple of things coming to mind are the joints in lever controlling the wastegates or the bypass valve that are a little dry or possibly a tear in the membrane of one of said actuators. For example the non-US cars that have a vacuum actuated EGR valve make similar whistle noises when the membrane cracks.

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