Computer noise

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Bill H
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Computer noise

Post by Bill H »

If my HP desktop computer runs silently for about an hour after powerup and then starts making a pulsating humming noise, low at first and then getting louder... Power supply do you think?

I had a hard disk failure once that was more of a grinding sound. This is different. It's is definitively a hum, not any grating or grinding component to it at all, pure humming.
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Weirdan
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Re: Computer noise

Post by Weirdan »

Depends on the tone.

Lower-pitch sounds usually indicate fan failure (fan speeds up and down, and generally rotates slower than it should). In this case you should either clean and oil the failing fan, or replace it altogether.

High-pitch sounds, barely audible but extremely irritating (and note that not every person might even hear it, especially older people due to natural hearing degradation occurring as you grow old) might indicate failed transformer in the power supply unit. This kind of problem generally solved by replacing entire PSU.
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califdon
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Re: Computer noise

Post by califdon »

Bill, it's probably the CIA tapping your phone. You gotta quit posting to those Al Qaeda forums!

Actually, I'm not a hardcore hardware guy, but I agree with Weirdan's observations. Check the fans first, that's probably easier, as well as the most likely suspect. The timing you described points to a thermal issue, so if you wait until you hear it, then quickly open the case (after unplugging the power, of course!), you might be able to detect where the heat is concentrated. Up here in the Bay Area, it would probably run fine--it's really c-o-l-d this morning!

Happy Holidays, everyone!
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Re: Computer noise

Post by Doug G »

You can usually see a fan problem with a flashlight. If a fan rotor is partially gummed up or the winding is partially shorted, you can visually see the blade is not spinning properly. Don't forget to check the cpu fan. Usually the only other moving part other than CD/DVD is the hard drive, and if the hard drive were making the noise you described you'd probably be seeing errors or problems in the software.
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Bill H
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Re: Computer noise

Post by Bill H »

I'm beginning to think fan. Case is not only not hot, but is cool to the touch, but I know that doesn't mean much. I'm guessing that there is a variable speed fan in there and as things warm up the fan speeds up to where it makes noise, cools things down to the point that it can slow down again... Wait, rinse, repeat.

I'm going to have to run the computer with the side off to check that out, but I'm guessing that with the side off it may not heat up enough.

It is pretty much definitely not the hard drive, and it doesn't really sound like the fan. There is just no harshness to it, or any trace of grinding like a bearing failure would have. It sounds exactly like a transformer humming, although why a power supply would do that intermittently, or to be more precise periodically, is beyond me.

I am going to open it up later today to check for dust and foreign material.

I did think of the gummint, Don, but I wasn't thinking CIA, more along the lines of the NSA. I don't post to Al Qaeda forums, but I think you've read my blog, so...
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social_experiment
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Re: Computer noise

Post by social_experiment »

Hard-drives (before or close-to crashing) tend to make a clicking sound which will be clearly audible
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Bill H
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Re: Computer noise

Post by Bill H »

Yes, clicking, or sometimes grinding. Definitely not that.

I have the case open as we speak. No significant amount of dust, no foreign material. Both case fan and cpu fan seem to be running normally, and both are silent at this point (after cold start). We will see. I have my stethoscope handy if needed.
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Bill H
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Re: Computer noise

Post by Bill H »

Must be temperature related, because after 2 hours and 30 minutes the noise has not started when running with the case open. Mumble, mumble, mumble. Is there a downside to just using the damned thing with the case open?
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califdon
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Re: Computer noise

Post by califdon »

The main downside is probably your wife's objection to its appearance. No, seriously, it makes it more vulnerable to dust, not to mention accidentally kicking it or having things (or liquids) spill into it. But for short periods, it would be pretty safe, I think. However, the thing that I would worry about is what the problem really is. Your stethoscope approach sounds good to me. If you can localize the buzz to a particular area (with the case on), that might narrow down the possibilities.
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califdon
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Re: Computer noise

Post by califdon »

I have now failed twice to remember to comment on this: I think a power supply transformer certainly could make such a sound, and it could be periodic, dependent on temperature. Such sounds are created as the windings move just slightly at the line frequency (60 Hz in San Diego, last time I checked) if the insulation and adhesive holding them in place become pliable, such as might be caused by heat. Another possibility would be that the transformer might not be firmly attached to the chassis to prevent any movement, but I don't see why that would be periodic.
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califdon
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Re: Computer noise

Post by califdon »

OK, one more factoid: can you compare the pitch of the hum with a musical instrument? On a piano, the A above middle C should be tuned to 440 Hz, so 3 octaves lower would be 55 Hz, quite close to 60 Hz. If you have a way to sound that very low A note, and if it sounds very close to the hum you hear, it would point to a transformer hum!
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Bill H
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Re: Computer noise

Post by Bill H »

Well, crap, it's definitely the case. I put the cover back on and the noise returned. I put my finger on top of the case and press down and it stops. Remove my finger and the hum is back. The screw holding the cover panel is as tight as it will go, so I apparently just need to sit about a one pound paper weight on top of the silly thing to solve the problem.
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califdon
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Re: Computer noise

Post by califdon »

Well, that may eliminate the hum, but something has clearly changed to cause it to vibrate and I would want to know what it is that changed! It's certainly frustrating, but I think you need to pin down the cause. Hey, if you were still on your old sub and you heard a new sound, you'd sure find out where it was coming from before the next dive, wouldn't you?! :-)
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Re: Computer noise

Post by Doug G »

If you can make the noise come and go by pushing on the case, probably something is just loose. Make sure there isn't some mounting screw coming loose.

There isn't really any problem with running a normal pc tower with the case side off, as long as you can keep from dropping old paper clips & such down in the works :)
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Weirdan
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Re: Computer noise

Post by Weirdan »

So this is a case of vibrating case after all :) One thing to check is that the case could be touching your desk with its side. As the case vibrates it would repeatedly come in contact with the desk, causing noises.

I had similar problem with my current case, though it was more like a chatter, not hum. Could be tricky to permanently solve it, however gentle kick usually solved this for a while. The problem mostly went away after I moved the system to SSD drive (SSDs do not vibrate as they have no moving parts, and my old HDD was the source of most vibrations).
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