Annoying whitenoise sound coming from snd_hda enabled chipset

[Yoshihiro Ota]

On Fri, 24 Jul 2009 01:23:18 +0200
Ståle Lyngaas <staale at lyngaas.com> wrote:

> On Sat, Feb 21, 2009 at 11:01 AM, Garrett Cooper<yanefbsd at gmail.com> wrote:
> >    I don't know how else to describe it, but when I turn up my
> > speakers enough (50%+) and don't have any sound playing, I hear a
> > whitenoise hiss coming out of them. When I change webpages (nvidia
> > driver is GIANT locked) or do something else kernel intensive it stops
> > for a brief second, but apart from that it's an annoying trill sound
> > almost like a mosquito humming around me waiting to be swatted.
> 
> I suspect this is due to the CPU executing the HLT instruction.
> 
> Try running the following command:
>     sysctl machdep.cpu_idle_hlt=0
> 
> -- 
> Ståle Lyngaas

I couldn't find such a sysctl.
The close one was machdep.cpu_hlt.

It looks I hear the sound for sure when disk is busy.
There are a couple other cases I hear the sound but the disk is idle.
It happens 8-BETA1/2 but not 7.1-RELEASE, though for sure.

Hiro