What EXACTLY causes banding?

Besides high ISO...

... what actually CAUSES the banding to occur?

my guess would be that the pixel charge is read from the top and bottom of the array (in an alternating/groups way) and slight variations in the amplifiers cause the sensor "strings" to differentiate themselves at greater levels of amplification (read ISO). while i don't have much experience with image sensors, i have worked on other types of products that work in a similar way... so this would be my interpretation of what is actually going on.

RF interference can also cause banding in certain situations.

I happen to know that one cause is a flaw in the camera.

This is from a MKIIN I returned because of he problem.

And here I thought it had to do with too many musical instruments.

Gotta realize that each pixel's 'data' is nothing more than a tiny overly sensitive electrical charge. With ISO increasing the sensitiveness of the sensor, it would not surprise me if the mechanism increasing that sensitivity itself, ends up creating a leaking wave interference, that repeats itself, creating those lines every so often.

Good question though, I am sure there are many specific technical aspects to it.

gasrocks wrote in post #6253277
And here I thought it had to do with too many musical instruments.

ROFL!!

I'd like to know also. I have a 1D Classic and it gets banding when using exposure compensation especially, and it shows most in the dark areas.