Sometimes it is acoustic coupling of a fan to the supporting chassis or to a
wooden desk top acting as a drum head that increases a fan annoyance factor.
You can modify a fan's mounting by using rubber grommets and insulation foam
to isolate its edge and screws from the metal chassis. This should decouple
the most annoying direct mechanical coupling.
Now if what you hear in headphones is modulated onto the audio, you need to
twist the DC leads to fans, and possibly shield the leads, with shield
grounded to avoid electrical coupling. However, I suspect you meant that
the noise penetrates even when using phones, to the ear.
GL,
Stuart
K5KVH
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