Regular over-extrusion..? Can anyone explain to me why I'm getting regular over-extrusion patterns on this extrusion calibration cube?

Just upgraded the extruder from stock to Flexion HT on my Balco Touch (Wanhao i3 plus) and now I'm getting a strange pattern on my prints.

The photos below show me trying to calibrate the extrusion multiplier after completing the extruder install.  The first is with a factor of 1 and the second with an adjusted factor of 0.86 (which I suspect is the reason for the change in pattern?).

I guess this is some kind of mechanical issue causing the over-extrusion?  Any ideas?



Note: during the second print (below) I was playing with the Flexion extruder's Cam set screw hence why it stopped extruding all together.  I tried it set tight and loose and other than when really tight and stopping the extrusion there was no real difference in the pattern when extruding.



Help..!
Mine is a shot in the dark, but the fact the overextrusion is so regular let me think it is due to something rotating going around in cycles.

The fact that the pattern changes with the flow parameter make me think the culprit is the stepper motor pushing the filament (as different flow means different number of rotations for the same lenght of printed wall).

A possibility could be an irregularity in the cobbed wheel biting it the filament: a longer tooth would push more filament into the hot end, for example.

Another cause could be a problem in the actual stepper motor, in which a failure in the coils causes it to move to steps instead of one, at some point.

There are possibly other suspects in firmware settings and stepper dirivers, but that's not the area of 3D printing I am most expert in.

Much more unlikely, it could be a defect in the filament, but that's easy to test: just swap it for another one!