[r67cat]

Always difficult to diagnose via a video, that said my suspicion is exhaust leak. Particularly telling is the fact that you noticed it after the header removal. I would not reuse the exhaust gaskets. For the hassle of removing the headers I would renew each time. Also with the hood closed, having the noise more noticeable, and certainly more noticeable near the side vents leads me to the exhaust gas leak. That often is mistaken for lifter noise. Rick