I usually spend most of time using on my laptop with its AC-adapter plugged in and running off the mains. My first prolonged usage on battery power alone was today.

Soon after, it came to my attention that there was a rather inconsistent high-pitched sound emitting from the laptop, which bothered me enough to start investigating. It didn’t quite sound like the creek of a hard disk, nor the whirl of a fan. I pressed my ear around the chassis, listening as I went, until I zeroed it in, at about the center of the laptop. Curiously the only component that I could think of as being there was the processor. But a processor emitting sound? That’s just crazy talk. Or is it?

It turns out, after searching around Google and reading threads on forums with similar complains and lots of skepticism from people who claim not to hear it, or maybe, they just can’t hear it, during to the difference in hearing abilities across individuals, the sound did indeed originate from the processor.

An article on Dell’s site explained it quite clearly. Quoting from the article itself,

The noise has been isolated to the processor’s power circuit and is only audible when the processor is in C3 (clock-stopped) power state. In this state, the computer is in a low-power mode designed to reduce chassis heat and extend the battery life. The changes to the components in the processor’s power circuit are caused by a phenomenon referred to as the Piezoelectric Effect. When a specific voltage is applied to these components, they begin to resonate producing sounds that fall within the range of human hearing (15 – 20 KHz).

C0 to C3 are power states of the processor, with C0 being the default functional state, and C1 through C3 being in various stages of power save. Simply put, the performance of the processor is scaled down in preference of a longer battery life.

To check the validity of the explanation, I launched Battlefield: Bad Company 2 and entered into a game, and sure enough, the noise was gone. Exiting it and waiting for a few seconds brought it back yet again.

With the cause of the problem uncovered, my next course of action was to disable the various power saving modes. Unfortunately, the BIOS settings on my laptop are minimal, and the option was nonexistent.

Trying a rather radical approach, I removed the ACPI-related drivers and rebooted. These drivers help expose hardware configuration and power management settings to the operating system so that they could be software-controlled. Sure enough, I can now run on battery without the annoying high-pitched buzz. However, the flipside to that was that the function keys no longer work, nor the screen off feature associated with closing the lid. Quite an unacceptable compromise. Resigned, I installed the ACPI related drivers back.

I didn’t fully comprehend what the Piezoelectric Effect was, neither did I manage to stop the annoying high-pitched sound, but at least I rest assured that my laptop isn’t about explode on me, or that I am going crazy.