Anomaly on walls of printed model

Hello Friends!
After spending several hours fine-tuning settings to get a good first layer with PETG I have developed a different issue. The walls of the model (vertical surfaces) are wavy, not along the X or Y axis, but along the Z-axis. I have not seen this before now. I spent the last hour or so scanning posts here and understand that certain print speeds may be at a speed that can cause a resonance from the stepper motors. I’m retrying a print with slower speeds just to see if that is the issue but I thought I would post a photo here for feedback as well.

Settings for this print:
Slicer: Cura
Material: Overture PETG
Print Speed: 50 mm/sec
Print Temp: 235
Bed Temp: 90
Cooling Fan: OFF
Layer Height: 0.2 mm

Thank you in advance for your thoughts!

I found the problem. I had the filament spool mounted outside the enclosure and there was some resistance on it. There was also a slight tangle on the spool as well. By resolving those issues the wall quality is back to normal.

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