Good info, however doesn't really explain why it is rattling? Surely every car with a vacuum wastegate doesn't make this sound?
It’s rattling because the wastegate is open by default instead of being closed. When it’s open the gate isn’t resting against anything, when it’s shut it is resting against something and can’t move.
The pulses from the firing order when the gate is open create the ticking noise. It’s all harmonics.