Cyclical rattling/buzzing sound coming from a Wades

Has anyone heard this cyclical rattling/buzzing sound coming from a Wades? ...
[vid.me]

I've tightened and looked at every part of the extruder and cannot find it. I do know it's related to the big gear; the rattle will repeat when the gear comes back around to the same spot.

Also, it does not do it much on perimeters; just mostly on back-and-forth infill.

Perhaps the gear is more worn down at that spot? If it's loose then the vibration from the motors could cause the gears to resonate.

The gears are tight with no free movement at any point in the rotation.

Maybe the X bearings?