Low-Frequency Interference Caused by Ground Loops

Hello everyone. I am using a stepper motor with an encoder (https://www.oyostepper.com/category-36-b0-Stepper-Motor-w-Encoder.html). To improve noise immunity, I connected the shield of the encoder signal cable to the ground at both the encoder end and the driver end. However, this has caused occasional extra pulse counts during low-speed operation, leading to slight, jittery fluctuations in the coordinates displayed on the CNC screen.

Using an oscilloscope to examine the A/B signals, I observed low-frequency interference—around 50 Hz—superimposed on the waveforms.

According to the technical documentation I've consulted, grounding both ends creates a "ground loop." The potential difference between the two ground points causes a circulating current to flow through the shield, which then couples into the signal lines.

The interference disappeared after I switched to a single-ended ground connection. I would like to ask: should the encoder cable shield be grounded at one end or both ends? And if it should be grounded at only one end, which side is preferable—the encoder side or the driver side?

Thank you.