HELP PLEASE. Stepper motor problem

Hi, I'm hoping somebody can help me with a stepper motor issue. My CNC has a nema 23 on the x axis. I has been working fine till recently.
The stepper motor runs very nice when jogging however it continues to move slightly when in hold position almost like its randomly twitching but the DRO in mach 3 shows it holding position. When the CNC is sitting idle it can move as much as 3-4 inched in a couple minutes. Thank You Kindly.

The stepper motor operates according to the frequency and number of input pulses. When the stepper motor is at low speed, due to low pulse frequency, it will vibrate during operation. Generally, at low speed, the stepping Angle is subdivided to improve the pulse frequency and the vibration will be improved