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Some component in my computer emits an annoying high pitched sound, like a constant screetching. I'd really like to dampen the sound while providing enough air flow for the computer. The computer is wedged between my desk and the side of a drawer cabinet, so I can suspend some material there. But everything I tried so far didn't noticably reduce the sound.

I tried blister foil, several sheets of corrogated cardboard and a piece of foam that was unfortunately too small. I even read some scientific studies about high frequency sound insulation, but they are written from an industrial point of view and suggest thick MDF boards as the best insulator.

Before I buy bulky packs of materials that may not work after all, I'd like to ask: Which material that a hobby crafter might have at hand acts well as an acoustic insulator for high frequencies?

P.S.: Of course replacing the problematic component would fix the noise problem, but let's assume that's impossible (at least short term) for the sake of the question.

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    Dusty cooling fans, tape drives, optical drives, and some hard drives can be problematic over time and should be retired before they fail entirely. Identify the troublemaker by unplugging and replugging one component at a time until you find the offender.
    – Stan
    Oct 15, 2019 at 0:38
  • Sound waves travel through air, which means if there's an opening for ventilation, then the sound is going to come through there. Blocking sound while allowing ventilation is really hard. A simple example is a door in a house: if it's fully closed, the amount of sound-dampening is significantly higher than if it's even slightly ajar. That's because a slightly-ajar door allows air (and sound waves) to flow through the crack, while a completely-closed door stops the air (and sound) flow and requires the sound to travel through the physical door itself. Fixing the computer might be the way to go.
    – BrettFromLA
    Oct 15, 2019 at 18:20
  • Is your computer monitor a flat screen or a CRT? The latter are known to produce a high-pitch sound from the horizontal sweep circuit.
    – Mike Waters
    Oct 25, 2019 at 4:57
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    @MikeWaters It's a flat screen. The sound comes from the actual computer case without a doubt.
    – Elmy
    Oct 25, 2019 at 5:06
  • In that case, what @Stan said is good. In my experience, it is most likely a fan.
    – Mike Waters
    Oct 25, 2019 at 14:41

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Usually, a high-pitched sound from electronics is due to something resonating. It may well be possible to kill the sound at source by breaking the resonance. If a component is emitting sound due to magnetostriction you can dampen the oscillation.

I have had success in the past by simply putting a blob of blu-tack or similar substance on the offending component.
If you can't identify the component or it is likely to be too hot, try parts of the circuit board itself. Often it will be the metal case of the power supply that is resonating, blu-tack will easily kill that source of noise.

This was a very common trick back in the days of 8-bit computers. Also, the line transformers of old CRT TVs could be susceptible to magnetostriction but at least the volume of the whistle could be reduced.

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Note: I think there is not much you can do to lower that sound. I mean something really practical. I do not have experience with noise-reducing headphones, and I do not know if they are suitable for those frequencies.

The most likely components that generate that noise are:

  • the power supply;
  • the audio hardware - cheap or not enough capacitors installed;
  • the HDD-related hardware.

The power supply

It is "easy" to rule this out by temporarily swapping the power supply with another one, from a non-noisy computer. If the sound goes away, then it is time for a new power supply.

Note that this sound might indicate the end of life of the said component, and when power supplies die, they tend to take with them other components too: motherboard, processor, hard-drives... Only God knows how voltages will jump around.

If this is the case, please replace the power supply ASAP, before something unrepairable happens - think about losing all your data - the one which you cannot download again from anywhere.

The audio hardware

Temporarily disable the audio hardware from the BIOS. Or using the dedicated hardware jumper on the motherboard. Read the documentation of the motherboard on how to do that.

If the problem is here, there is not much you can do. Replace the motherboard, or just leave the audio hardware disabled and purchase a stand-alone sound card.

The HDD-related hardware

Disconnect all hard-drives (both power and data). Maybe use a live CD / CD to boot some OS (Windows or Linux). If the sound goes away, you are in for a new motherboard.

NOTE: there might be several sources of noise. You might want to disable everything first, and then enable them one by one, until you find all the noise generators.

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This article Practical Soundproofing discusses the difficulties of providing sound insulation.

A successful hack might find other ways, such as neutralising the sound electronically, as discussed in the Wikipedia article Active noise control. One system on the market is noise cancelling headphones or buds, though there are practical disadvantages. Other systems are under development, such as Sono.

Or, find and replace the screeching computer component.

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To reduce the noise coming from your computer, you have to enclose the entire computer in a box. This box must have fairly thick walls of a sound-deadening material (MDF is easy to work with). But you can't just build a box: the computer needs airflow in and out. So you have to build passages for the air. A labyrinth will allow air to pass through but reduces the noise, but takes up a lot of space. The labyrinth walls need to be covered in sound-deadening material.

If your computer is wedged between two objects already, there's little space to accomplish what you want.

It takes far less time to replace the offending component than to build a custom box.

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I got a microfiber body towel at the Diaso (Japanese dollar store), folded it over itself and hung it in front of my 1U pfSense router in the front of the enclosure with office clips that can be used with screws and it reduced the fan noise by over 50%. I also got Noctua fans beforehand which removed the failing bearing sound but were still actually quite loud. In theory you could get the magnets with holes in it and put the clips and magnets together. I also caution that you leave no less that 3 inches of space between the towel and fans for a normal fan and 6+ inches for industrial fans and I don't mean the Noctua ones I mean the ones that come in Workstations and Servers or anything capable of moving 100+ cfm.

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