Z Axis Upgrade W/ 269oz NEMA 23 Stepper

It is. The mechanical connection is rigid so each step start/stop is “seen” by the assembly and this makes it vibrate.
Smaller steps mitigate this phenomenon. So will faster acceleration values / rapids also as it lessen the time spent at slow movement.

Imagine the feed is like 3mm / min, each step will have time to initiate and terminate motion before next step occur, causes a “jagged” motion.