> I can remember one particularly strange incident where I could here noises
> when I was running a CPU intensive job (raytracing) as opposed to the machine
> being idle. I can only guess I am hearing subharmonics of the bus traffic but
> I find that hard to believe.
I used to 'monitor' the bus traffic with a cheap radio. That's about
the right frequency. ~100MHz electromagnetic.
You mention ~5kHz acoustic waves. They might come from the switching
power supply. The power supply adjusts the frequency of switching
to the current that is needed by the CPU. An idle CPU needs (much)
less current than an running one.
(Btw: Has anyone made measurements how much Energy every command
of a CPU needs? Idea: A compiler switch for low-power code!
I measured that my computer needs 1.3amps when booting and 1.0amps
when idle.)
Christoph
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