In some higher current steppers, usually when the motors are wired in parallel, you may notice a high pitched squealing. This is possibly due to the high amount of current passing through the windings. If you are using a Zeta or Gemini GT drive, audible noise can be lessened, and possibly eliminated, by enabling Electronic Viscosity. On the Zeta drive/controllers (Zeta61xx) and the Gemini GT and GT6 drives, this is accomplished through software with the DELVIS command. A setting of 1 or 2 is usually sufficient to reduce noise. The default setting is 0. On the Zeta drive-only, there is a small rotary switch that you can set between 0 and 10, but only settings 0-7 work and have effect. . If you set EV too high, it can have adverse effects on performance. Bottom line... too little is better than too much. EV only takes effect below 3rps.
For more on Electronic Viscosity, see the Zeta4 Installation Guide.