2.7L fluttering noise on low throttle

[OF Hero]

Hey all, recently started parking in a new underground garage for work so I'm getting a ton of new/interesting echos and reverberations off walls, so I'm unsure if this is a new/normal sound, but I'm getting this low speed/throttle fluttering noise that only happens at a certain very low throttle input. I'll get a video of it up later but it sounds very much like a baseball card in bike spokes. Truck drives fine otherwise, 10k miles.

I don't think it's cam phasers since it has nothing to do with startup or engine temps, again very specific at a low throttle input. Cant be wastegate noise, turbos aren't engaging at such low RPMs.

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