Extruder consistently inconsistent when printing

[Zimm]

Ok to start I have a Creatbot D600 Pro that I have now upgraded with a Duet Wifi and duel E3d Hemera extruders. All calibrated to E3Ds spec and running perfectly except for what I can only describe as a consistently inconstant print problem. See attached photos. my prints end up with a consistent banding through them. At first I though it was a Z hight problem but on closer inspection the banding changed depending on the distance printed per layer so there for it had to be an extrusion issue. Yesterday I printed a large prototype for a client and I noticed the problem on a large base layer. Also see photos. I can not find anything on the net to explain this problem. Has anyone had or seen this issue before?!

[Phaedrux]

Can you share some more info?

What firmware version?
What are the motors and their specs?
What current are you running them at?
Does it affect both extruders?
Also post your config.g

Something cyclical like that definitely seems to be extrusion related. Have you tested other filament in case its a regular variation in filament thickness?

[Zimm]

See attached screen shots. Both extruders have exactly the same issue. And I have tried around six different medias and all good quality. I though it could have been a variation in filament too.

[Phaedrux]

What is the filament spool mount situation like? Does it roll smoothly or is there tugging?

Are you able to do a vase mode print to see if you can make it apparent on the surface? Maybe the period of the artifact would give an indication of a possible cause.

It's odd that both extruders has it.

Maybe it is a form of Z banding. Have you PID tuned the bed heater?

[Zimm]

The third photo of the white prints are in vase mode and around 300mm square. The paten is defiantly uniform. The only issue with this is that the larger the diameter the closer the banding is and as it narrows towards the top the banding gets further apart. This is really accentuated on a few prints that have been hollow up to a point where i have added a 20% infill. Then the banding instantly gets tighter. Ill see if I can find a failed print that shows this.