What exactly is producing the ‘ratcheting’ sound a computer makes when it’s working/processing info?
I’d always thought it was the sound of the hard drive spinning.
It’s the hard drive head changing direction.
What Skip said.
What is the churning sound I hear from my hard drive whenever it is retrieving data?
Fans.
HDDs. BTW, HDD R/W heads don’t change direction. They just slide in and out radiacally on an assembly.
The main noise a computer makes is its fan. The hard drive spinning is also audible, but much quieter than the fan.
On more than one computer, when I start a long computation, I hear a high pitched noise, like a whine but with more structure to it. This is definitely not the hard drive noise. Any ideas for this one?
high load on the cpu increases temps. maybe you have a temperature controlled fan… aka higher temps = higher fan rpms.
Three main sources:
- The power supply fan - usually constant, unless there’s a problem. When these fans go bad, they often have an out-of-balance type of sound.
- The CPU fan - most times constant, although some have variable speeds. If variable, the whine should change gradually.
- The hard drive - a constant whine when not in use (spinning but idle), and anywhere from a light chatter to a sound akin to bees in a can when the read heads are jumping around from place to place.
CD/Floppy/Zip and other removable media drives have their own noises while in use, but those are usually easy to identify.
Most sounds are benign, even if they’re annoying. A missing sound is usually an indication of a problem.
Slide in, direction: towards the center.
Slide out, direction: away from the center.
Sounds like changing directions to me.
And the sudden change is what makes part of the noise.
-CD drives make a whirring to loud whooshing noise from spinning.
-Temperature controlled fans spin up and down yeah… Typically only laptops have this type of fan, but my Dell GX150 (a micro-tower style) has this type too.
-Your speakers have a base level of noise that’s coming from them
-Your monitor runs at high voltage with huge capacitors in them, which is why it has that high-pitch whine like your camera flash and tv.
BTW, I don’t think HD heads have slid in/out since you needed a metre stick to measure the platter size… older 5 1/4 style drives used a stepper motor to move the head assembly back & forth, but every drive today (including the 3 I’ve taken apart) have the voice-coil style head assembly like this. (PSA: if you take the magnets out, be careful not to pinch yourself in them.)
In the link posted by Nanoda, you can clearly see the head in different positions in different photographs. The arm with the read/write head on it most certainly moves from the edge of a disk towards the centre. This is very similar to the way the read/write laser in a CD rom moves to read data off different parts of the disk.
If your hard drive is an IBM DeskStar, and hear a grinding noise at random intervals, you might have the “Click of Death” problem.
Yeah… if you want storage space w/o the overhead, you need a read head to move back and forth on a spinning medium. In the old-old-old days, there was 1 head per track, and only the platter moved. For a random example, Maxtor’s current drives now have 27,000 tracks per inch. Not very feasible.
HD heads whip back and forth in an arc, controlled by a magnetic field at the other end. (That’s what the magnets are for).
A CDrom has only 1 laser head, and it does slide in and out on a rail (the assembly is much bigger and heavier), as it frequently only has to read slowly outwards (CDs are recorded inner hub to outer edge), and even if it doesn’t, speed isn’t a big deal. You can hear that thing move over the whoosh of the spinning CD when you install a game usually.
Such information to be gleaned just from all the different noises your machine makes. Perhaps all computer techs should get stethoscopes. 
Could be noise from your system bus leaking out of the sound card (more likely with a cheap or onboard sound card). Does the noise go away if you turn off your speakers?
I had a laptop that made very distinct sounds like that… when it was idle, the whine was pretty constant; when it was working, it fluttered up and down in pitch; and when it was sorting something big, it started high and gradually came down in pitch until it was done.
One of the systems doesn’t have speakers. Anyway, the sound comes from the case.
My guess is it’s fan related. My Athlon 1800-based system is in a case with three fans - the CPU fan and two case fans. All three together produce a constant whine. You’re probably experiencing a similar pheonomenon.