[PLUG] Quiet intermittent beeping on Thinkpad T42

[Evan Heidtmann]

Hi all,

I come to you today with a very odd problem. My thinkpad is now making
an annoying low-volume sound that is very difficult to describe. I made
a recording:

http://evanheidtmann.info/audio/thinkpad-beeping.ogg

You will have to turn up your speakers a bit. It's a high pitched
beeping sound that is irregular, yet seems to have a pattern.

I can't tell if this sound is new, or whether it's been there all along.
I also can't tell for sure what part of the box it's coming from, but
the recording was made from a speaker. The same noise can be heard in
headphones attached to the laptop. The sound happens in Linux, but not
in the BIOS, GRUB, Windows, or the IBM Rescue & Recovery application.
The sound disappears when any constant CPU activity occurs: playing an
OGG (muted), moving the mouse around, scrolling, or holding down a key
(with autorepeat). It seems unrelated to display activity. The volume
decreases to an almost inaudible level when I reduce the CPU frequency
from 1700Mhz to 600Mhz.

Has anyone seen this before? Any suggestions for how to go about
eliminating it?

Thanks,
Evan