Magnetostriction is about a bulk material changing dimensionally with varying
magnetic field; this is probably not occurring or not the prime mechanism.
More likely, it's simply that the magnetic fields generate forces acting
on the currents in the coils, and the coils and neighboring structures are
not infinitely stiff, instead acting as a low efficiency speaker.
Another mechanism is piezoelectricity: the ability of materials
to undergo dimensional change as a result of static electrical fields.
I've seen high voltage capacitors piezoelectric enough to damage
their own leads over time.
Thermal effects in thin board traces can be fast enough also to be audible.
If you really want to find out what area of your PC is producing the sound,
use the auto mechanics trick of putting one end of a flexible hose to your
ear and the other end near a suspected sound source, taking the usual
precautions for your safety and your PC's.
This is a FAQ item though lesser priority.
Checking the archives at January 28, 1999 gives some discussion of
hardware-specific symptoms, and suggestions.
Earlier mentions are at August 15, 1996; December 9 1996; January 25 1997;
April 14, 1998.
At 03:24 PM 1999/07/22 -0500, "Willmore, David" <[EMAIL PROTECTED]> wrote:
>All,
>
>There are several things in a computer which will have their operational
>parameters vary with CPU activity. The most likely ones are: audio
>subsystem receiving noise coupled either directly (magnetically) into its
>signal lines or via its power feed; or the load on the power regulation unit
>itself. Yes, coils do can make a buzzing sound. The name of the phenomina
>is 'magnetorestrictance' (who wants to be I spelled that one wrong?) which
>is the property of a material to change its physical dimensions under
>varying magnetic fields--it's the reason large power transformers 'hum' and
>how most high power sonar units generate their signals.
>
>If I remember correctly, this is an IFAQ, but could go in the FAQ so that
>the-word-which-will-go-unmentioned can get spelled correctly once and for
>all.
>
>Cheers,
>David
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