High Pitched Whine

Joseph Koshy joseph.koshy at gmail.com
Mon Jun 5 23:26:43 PDT 2006

> When I am running FreeBSD, my computer emits a high pitched
> whining noise. It's not a 'physical' noise like a fan or hard
> disk grinding, it's more of a electrical whine.

The only thing that I can think of that could think of that
could whine is a flaky magnetic component.

Does the frequency of the whine change if you change HZ?
Does the whine reduce if the processor is fully compute

On an idle system, the processor should quickly go
back to sleep after handling the clock interrupt.
Since this should take a few uSecs at most, the processor's
power requirement surge should be handled by the reserves in
the power supply's output capacitors.

My guess is that FreeBSD's clock handling is taking long
enough that your SMPS needs to (briefly) increase its
current output.  This change in current output could
cause a whine if a magnetic coil in the SMPS was loose.

Someone with a spare 'scope could check this hypothesis
out ... if there's a correlation between the ripple on
the 5V line and the clock rate on an otherwise idle
system, then we're spending too many cycles in our clock

FreeBSD Volunteer,     http://people.freebsd.org/~jkoshy

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