PC sound effects
March 21, 2007 2:05 PM   Subscribe

How do I stop two PCs from turning themselves into a very annoying musical instrument?

We have two PCs in our study at home. Recently they both got upgraded after one got too hot and fried.

Both machines are slightly louder than I'd like, but I'll deal with that. The problems start when both machines are switched on at the same time.

Within a few seconds of the second machine powering up, there's a deep droning pulse starts with a frequency of about 1.5 seconds. My wife can barely hear it, but it's driving me mad.

I've tried killing various fans on the two machines but it doesn't affect the noise. Realistically, what are my options for killing this noise?

Both got upgraded with identical cases and Zalman CPU fans, twin front 80mm fans, single back 80mm fan. Otherwise, they're different, from the drives to the motherboards boards.
posted by twine42 to Computers & Internet (12 answers total) 1 user marked this as a favorite
Could it be vibrations from the fans/hard drives being conducted through the table that the PCs are on? Try some rubber feet and see if that makes a difference.
posted by chrisamiller at 2:24 PM on March 21, 2007

Response by poster: chris - I just picked one up and held it a foot above the desk. Still droning... Nice idea though.
posted by twine42 at 2:31 PM on March 21, 2007

Best answer: Probably a harmonic. I had a computer in my study - when it was on it wasn't too bad, but lying in bed with my head on the pillow, I could head this slow throbbing hum noise. Very annoying. Rubber padding helped, but what really helped was replacing the fans. It turned out to be the power supply fan.

There's a very busy `silent PC' community out there with a lot of good tips on quieting down your computer. Low speed fans, fanless power supplies etc can all help.
posted by tomble at 2:32 PM on March 21, 2007

Best answer: Sounds like some of the fans are making slightly different tones creating beats. Scroll down a bit and there's a neat animation demonstrating the effect.

Other than 'tuning' the offending fans (either so they're at the identical frequency or so that they're very different frequencies), I'm not sure there's much you can do. Alternatively you can buy quieter fans (higher quality parts) or larger fans (larger area, lower speed) to replace the louder of the current case fans.

posted by porpoise at 2:35 PM on March 21, 2007

One off-beat possibility, since the machines have recently undergone provocative maintenance:

Any possibly that the fan causing the beat is on a video card?

I have a video card fan dying at a clients'; it's fairly common, since they hang upside down from the card.
posted by baylink at 3:11 PM on March 21, 2007

Best answer: Alternatively, you can start a band.
posted by matildaben at 3:38 PM on March 21, 2007

I feel your pain. I have a loud video card. Ive just ordered a replacement for it.

Are you not able to power it up with the case open and determine which component the drone is emminating from?
posted by gergtreble at 3:50 PM on March 21, 2007

If the drone is pulsing at a 1.5 second rate, it's almost certainly due to the interaction between two fans, not coming from one fan alone. And the two fans concerned are probably the same model doing the same job, because they're running within 1/1.5/60 = 0.011 RPM of each other. You'll need to isolate which pair of fans is conspiring against your sanity, and replace one of them with a different model.

Turn off your second PC, then poke a matchstick through the fan blades on every single fan in the machine (CPU fan, video card fan, front case fans, rear case fan and power supply fan) to jam the fan, and turn it back on. If the drone is gone, pull out matchsticks one at a time until it comes back; the last fan you enabled will be beating with its opposite number in the first PC.

Obviously, running a PC with jammed fans for more than a minute or so is a Bad Idea.

If you still get the drone when you've jammed all the fans, the next most likely source is interacting CRT monitors. These all emit supersonic squeals at the line rate, and buzzes at the frame rate, from the deflection circuitry; if two nearby CRT's are running at very similar but not identical scan rates, they'll beat.

If it is CRT's, you should be able to kill the drone stone dead by running them at different refresh rates - set one to 75Hz and the other to 85Hz.
posted by flabdablet at 5:05 PM on March 21, 2007

Response by poster: The graphics cards have been in the machines for about 2 years I guess, and weren't causing problems before but I'll look at them tonight.

Only one of the machines is a CRT.

I'm now starting to wonder if it is actually the fans at all... I pulled the graphics card and all of the fans and the noise continues...
posted by twine42 at 1:23 AM on March 22, 2007

How did you go about pulling the power supply fans? They're usually soldered in. Did you jam them?
posted by flabdablet at 2:19 AM on March 22, 2007

Response by poster: doh... I pulled all the fans except the power supply fans.
posted by twine42 at 3:56 AM on March 22, 2007

Don't attempt to pull those, because you need to get inside the power supply to do so. Jam them instead. Do that while they're stopped - don't jam a moving fan, or you may break blades or end up with bits of matchstick inside your power supply.
posted by flabdablet at 12:40 AM on March 23, 2007

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