High Frequency Noise

MelissaJeanne used Ask the Experts™
I hope someone out there can help me.

I have a problem with a high frequency noise coming out of my computer box at an extremely high volume.

The biggest problem is that the frequency is out of the range that the average person can hear.

I don't have much to go on - but I hope this information will help describe it:

Many years ago I went through the same experience with a TV set. From the first time I turned it on the screech was unbearable. I had found out then that punching the TV enough to cause vibrations would make it cease for a couple of minutes. (not a solution for the computer!)

After a year, a guest walked into my house and immediately commented on how loud that noise was. He was a computer repairman and told of how they had a computer come into the shop with the same problem; at the insistence of the secretary who was the only person in the company who could hear it. But I do not recall what the source of the problem was.

I have taken the computer to the repair shop and I requested that diagnostics be done on the hardware but since no one there can hear the sound, they feel I am simply hearing the disk drive spin. They cleaned up the fan, but the sound is still present.

I can only describe it as characteristic of a florescent light bulb that is going bad. To those that can hear it, its well described as trying to drive a car with a loose fan belt; until I can properly communicate the problem to the repair shop, the computer is unusable.

If anyone has experienced this, or knows enough about electronics to suggest where I can tell the repair shop to troubleshoot, I would be grateful to hear your comments.

Thank you.

I feel this question is worth more than 75 points, but that is what I got at registration, so am offering them all up.
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Processors tha run at high speeds can put out a high very frequency when they operate. One way to hear this is to put a radio next to your computer tuned to an am station then turn on your computer.You will hear the distortion thru the radio.
I have never heard about this being loud enough to hear.It may bother animals though.The way to stop this is by shielding. the computer inside the case. Also if you use speakers with your computer they should be shielded speakers and any cables
you have plugged into your computer too. Power cords are ok
they are already shielded. I bet that you have something else on in that room that the sound is coming through. good luck!
>>Processors tha run at high speeds can put out a high very frequency when they operate.

Very true but no human being can hear this high.  I believe I read where someone could hear up to 25kHz or so.  Since today even the slowest CPUs run at speeds in excess of 1GHz, your assertion here is totally riduculous!

I suspect that you are hearing the SAME thing you've heard before coming from the CRT display.  These have a HORIZONTAL SWEEP frequency in the 15,000 - 20,000 Hz range depending on what display mode is selected.  Some displays are just plain noisy with various internal part that vibrate or resonate at the sweep freq.  Very annoying!

I suggest trying a different display mode and see if you can find one that gives a good image but does not irritate you.  Or perhaps try a different display.  The new LCD display DO NOT HAVE sweep circuitry and so are virtually slient even in the high-freq. audio range.


In the response to comments so far,

Thank you Vig12 for your input.
I have one point that does not pan out - both I and the other person in the house, who can hear this, confirmed the source of the sound is coming from inside the computer box.

However, I also found information on the net last night pointing out that parts within the box can act as an antenna of sorts, for surrounding noises, (the subject of the article was electrical noise). So I do not discount your thoughts on this at all. The idea of a shield may be a solution, which ever direction the noise is coming from.

We have been exploring as best we can removing printers, speakers, lamps, moving cords, etc. So far with no impact.

I will try your suggestion of altering the display mode as a troubleshooting tool, it sounds good, as you are correct in that my first reaction was that it was the monitor (because of the TV problem I experienced, and yes, I would put it in the family of those sounds). I don't know why your answer was so abrupt. There is no debate occurring here concerning the laws of physics or anyones ability to be ridiculous (note spelling).

I am merely describing a noise I and another can hear. This computer has run for over a year without a problem.

As additional information to my first question:

This comes as no surprise to me, that others are not hearing it, or thinking I am imagining it. I have been through this before with the TV.

Also, I was given an intense hearing exam in my adult life, they made me retake it under someone else and I was told, "there is nothing to report except that you went off our pre-printed charts in both directions in both ears".

Also, I should mention that I have owned home computers since the early 1980s and have used them regularly at work. I know the sounds to expect and am comfortable, even with old equipment.

That is to say that is a sound at a loud volume, I am not being over sensitive to normal noise.

Perhaps I need to explore a means to measure the volume? Any ideas? The computer is under complete warranty - that may be my only means to prove there is a loud noise...
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Hi MelissaJeanne
Many if not all computers now use power supplies based on switch-mode technology. These are designed to give a higher output capability in relation to the power the consume. They do this by rectifying the mains in then 'switching' this through a step-up transformer to around 4500volts (hence the warning on the side). Now by the laws governing transformers the higher the difference in primary to secondary voltage the greater the current available. On your original question, the transformer used operates at a very high frequency (differs between power supplies), they are usually made of laminated iron plates with the coils wrapped around the plates. If the lamination cracks you can have a loose plate which can vibrate at the same frequency as the switching. This will produce the noise you describe. There is also suppression capacitors and inductors arranged around the transformer circuitry, they are there to suppress harmonic generation. Again failure of one of these components will lead to high frequency noise generation.
In short do you have another power supply available to try?

Hi MelissaJeanne,

don't know what's your system installed but here some tips about noisy boxes :

- be sure that every screws is correctly fixed (on chassis, PSU, CPU Fan, cooler, motherbaord etc..)
- some CPU fans may increase there speed regarding the temperature of the system. If you have a big cooler enough you may put instead a PSU or box fan which have stable speed on the CPU (I did, perfect for me :-) )
- some fan are not well fixed to the cooler or are to close, and some may need an additional thermal batter between the fan and cooling system to be placed to avoid noise
- PSU fan has been cleaned, CPU fan also?
- does the noise appear if you only use the unit in DOS mode, or only under windows? If under windows, it means that you may have a power management tool that may require an upgrade..
- are you sure the noise is not coming from internal speaker? (you can listen "in" your tower ;-) when noise is on, except if you have kind of small form)

Otherwise you can precise if the noise starts as soon as your computer starts or not, and to eliminate the monitor, just turn the monitor off when noise is on.
Hope I helped!

Glen A.IT Project Manager

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