On Sun, 11 May 2003 23:28:25 +1200, Andrew McGregor <andrew@indranet.co.nz>  said:

> cpufreq and speedstep don't work on Dell P3 laptops anyway, and the 
> *internal power supplies* of the i8x00 series make wierd noises when APM 
> tries to idle the CPU.  The board will do this anyway, without making 
> noise, so linux need not.

Dell Latitude C840 (1.6G Pentium4 Mobile) has the "power supplies buzz at 1Khz
on APM idle" symptom too. I haven't checked the ACPI side of the fence yet, nor
have I gotten brave enough to try the cpufreq and speedstep stuff.

Even *more* bizarre, there's "something odd" done by the seti@home client
(which usually causes 100% CPU use and thus silence) several minutes into a
workunit that causes  the noise to change frequencies - it will start down
around 500hz, sweep up to 1Khz (taking about 2 seconds to do so), and repeat
(so the buzzing is exhibiting a sawtooth wave).  I'm not seeing any paging
or swapping or I/O, so I'm wondering if it's some code walking through a large
array with strides 1/2/4/8/16 (like an FFT) causing different cache hit ratios,
and thus different power consumption patterns while it's stuck on a L1/L2
cache miss.....