I don't know if the 3 pages of discussion of specific components from 2005-2008 is really useful. I guess SPCR does not mind boring the snot out of newbies.
In music recording, you need to sample twice as fast as the highest frequency that you want to be able to reproduce. CD music only sample at 44khz, but most MP3s only sample at 32khz or even 22khz. Many people do not notice that every sound with a frequency above 11khz has been removed.
Most people (particularly old folks) don't hear high frequencies well. Young people and the (un) lucky can hear frequencies up to 20,000 Hz (20khz).
Scrolling through web pages - Makes a gritty noise when scrolling though pages fast[...]
Loading screens - It's the most noticeable in Crysis[...]
Both of these activities have a spots of higher load then idle.
Here's the puzzler. I play WoW in windowed mode so I can surf browsers on the side and watch hulu. After I log in and get to the character select screen, really bad whine. But if I click out of the WoW window and onto the desktop or a web browser or anything else, the whine immediately stops. Now the 3D character is still in the windowed WoW frame, still apparently rendering smooth and fine. I click back into WoW, selecting the game, and the whining starts back up as WoW becomes the active window. Click off to another window, and the whining stops... completely.
Again, this is load. In windowed mode, WoW drops the frame rate to 20 fps (AFAIR). In most systems, this means that the CPU and GPU drop into a lower-power state.
I can't tell exactly where the whine is coming from. I think it's coming from either the video card or perhaps the MB near the CPU. Both of which are in the same area. The CPU area is cramped by a giant cooler, and the video card is boxed in the standard factory shell. Obviously the whine is directly tied to my video card, so if it's not coming from the video card itself it's off the MB power coils feeding the PCI-e lane. Right?
Your power supply will be switching in the range of 50 kHz to 1 MHz. They will hit a transistor that switches voltage swing direction, and then charge a DC capacitor, etc. The power supply then has more switches to feed the specific lines to your system.
I expect that the coil noise can be from a component, or a set of components where their power supplies and power draws cause this 50kHz-1MHz noise to drop into the perceivable range.
If you read about CPU power supply phases work, you realize that not all of them are in use all of the time. They are turned on and off depending on load. The CPU can switch from one to the next in a fraction of a second.So if you have a power supply that is running at 100kHz, and you have a CPU power supply that is hitting its fourth phase at 5kHz, you might hear a buzz at 20kHz due to the interaction of power supplies.
This could happen inside one component that produces multiple outputs. A main board produces CPU, RAM, and "South Bridge" voltages. A graphics card produces GPU and RAM voltages. A power supply produces 12v 5v 3.3v, -3.3v and -5v (AFAIR). With all the interactions, you might have a hard time hunting down the component(s) responsible.
As high-frequency noise does not travel far, I would solve this with distance
. A long HDMI cable, USB audio, and a USB extender (or two) should put you 40 ft. from the noise.
Most facts are from Wikipedia:http://en.wikipedia.org/wiki/Hearing_range
Also try moving your computer to another direction/distance from your head:http://en.wikipedia.org/wiki/Sound_localizationEDIT:
If Mike Chan and Gabriel Torres (of hardwaresecrets.com)
had a weekend together with all their tools & toys, I bet they could make a good article about this process.