Given that its throttle-related and not speed-related I would say it's forward of the flywheel and not something rotating. The way it behaves with the accelerator pedal says vacuum / intake leak to me.
The manifold pods might actually be a clue - if one of them has a split diaphragm it could be making a noise as its leaking. Possibly it could be a leak in part of the SAI valve system which reduces the vacuum such that only one pod can activate. Possibly something around the throttle body boot / oil separator.
I would first try disconnecting the vac pod solenoid valve, just to rule those out. It will throw a code but thats easily cleared. If that doesn't affect it, have a good look around the back of the engine with a torch looking for split hoses.
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