Take this troubleshooting with a grain of salt. I am no expert on yokes, but a friend and I have removed them. So I'm not completely clueless.
I notice the buzzing getting louder when you turn the camera towards the front of the yoke, as if the sound is being amplified by its cone shape.
If I'm correct, that would point to something in the back creating that sound before it enters the cone.
I can probably unplug the yoke and confirm that the sound ceases. But I think it’s the yoke, it’s easier to distinguish in person. But hey I have to unplug the yoke anyway right?