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        Fri, 12 Feb 2016 13:46:15 -0800 (PST)
Date: Fri, 12 Feb 2016 22:46:10 +0100
From: "Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Stepper Driver Question
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Precedence: bulk

> Could be the PWM it uses to control current through the coils
> (remember, steppers have to be powered all the time to avoid losing
> steps, even when stopped).  Check with a scope and see if it matches
> the spec.
> 
> You might be able to silence it with some extra inductance in the
> wires, either a LC low-pass filter or a ferrite, depending on your
> design needs.

It is normal for switched power electronics to make sound. Either from the switching or the control loop.