What else can cause X-Shifting that I haven't investigated yet?  

What else can cause X-Shifting that I haven't investigated yet?

Prusa Mk4 (1 month old)
Firmware 5.1.2+13478
PrusaSlicer 2.7.1
eSun PETG @ 230/90
Nozzle: 0.4mm
Input Shaping: On
In original enclosure, on concrete slap.
Temperature stable around 30c

I am getting x-axis shifting. Anything between 1mm and 15mm, so far, and can be in either direction.

It doesn't affect all models, but it can happen at any layer, and it doesn't repeat on the same model.

• This happens on both 0.1mm layers, and 0.2mm.
• Calibration all passes fine.
• GT2-16 pulley screws both tight.
• Belt is correct tension and doesn't slip when I try to manually move it
• Belt looks visibly fine, and no debris.
• GCode looks fine - and is transmitted from PrusaSlicer so no USB to cause issues.
• Filament is dry, and fed from a filament dryer.
• Extrusion calibrated @ 0.97
• Lowering print speed doesn't appear to help
• Increasing lift height doesn't appear to help

Could I be looking at a faulty motor here?

Or what else could cause this because I'm stumped and sad