Do computers give out a high frequency sound?

Could be the monitor. I've noticed some will whine at different resolution rates.

Some HD motors also whine.

Course, after 100-odd concerts at close range, many of the higher freqs are sometimes lost to me. 🙂

Could it be something the cats can hera and we can't? Sure.
Cat/dog (and kid) hearing is waay more sensitive than ours -
Recall those articles about shops that put in UHF emitters to drive the loitering kids off, but adults couldn't hear the sound? (And now kids are now using it as a ringtone?)

Another thought...
When you turn on the machine, or go into the room (and turn on the lights)? I ask b/c in my house, a specific brand of light bulb always emitted a high pitch whine.

I changed to a different brand, the whine stopped.

They can. Esp. if you're using a Mac Book Pro. The "whine" is a well known problem with them.

Really, though, it could be almost anything that's causing the sound... if it is coming from something inside the computer, then you're not going to be able to get rid of it and I doubt Apple will be willing to do anything for you. Your cats aren't covered under AppleCare after all. 🙂

That having been said, there are some thing you can try... starting with moving the computer. If it's in the corner, move it to the wall. If it's against a wall move it out a few inches. Try hanging a soft wall covering up on the wall, temporarily at first, to see if that'll help absorb the sound. A quilt, a bedsheet, any "egg carton foam" you have laying around, anything will do.

As a last resort, buy your cats earplugs.

A lot of things can give out a high frequency sound that some creatures can hear and some can't. TV's, Monitors, hard drives, all are capable of doing so, especially CRT TVs/Monitors. I noticed your listed computer is an iMac; is it a flat screen iMac or an older CRT iMac? If it's the latter, I would guess that the whine that the screen gives is what is making your kitties go bonkers.

A few solutions come to mind. I had this problem with a TV awhile back, and for some reason, just changing which outlet it was in seemed to do the trick. A TV on my campus had this issue for the longest time, though this time it affected certain people instead of cats; they left the TV off for about 2 weeks or so while they tried to figure out who to go to in order to get it fixed. A clueless student didn't read the sign on the TV, plugged it back in and turned it on, and the sound was gone. finally, and this seemed to work best for my kitties when my TV was whining...I got them a lot of catnip; they stopped caring about the noise eventually.

See if this answers your question:

Below you can find a few tips on reducing computer noise. But first, let's look a bit into what computer noise is, and what are its effects and why do we need to reduce computer noise.

Your computer generates a lot of 'pollution' around it. Not only it generates magnetic fields, radio frecquency emissions of various wavelengths and such, it also generates noise. Computer noise can be dangerous for your health and generate permanent damage. Getting back to computer noise itself, there are two types of noise. The first type is the noise generated by computer fans. Modern computers are using a lot of power (already too much power, in our opinion) so they get heated a lot and they need many cooler fans in order to remain at a decent temperature and not get fried. There are cpu fans, power supply fans, and lately there are such cooling fans installed on various components like video cards, hard drive units and removable storage units, etc. These fans generate noise due to rotation of their blades. There is also noise generated by storage units like hard drives and cd-roms. Probably the most important noise of this sort is hard drive noise. Modern hard drive units have high rotation speeds, up to 10,000 rotations per minute, and many of them generate a lot of high-pitch noise. There are other types of computer noise as well, for example some power supply units can generate high pitch noise as well that can be anoying for some computer users. One over another, all these noises are polluting our room and it is quite nice to see how we can get rid of them.

Well, there is no solution to completely remove computer noise - not yet. There are a few cooling systems that do not use fans and rely only on massive heat sinks made of metal, particularly copper, but they are not too effective in case of modern high speed processors because these processors actually need a lot of air flow going in and out the computer case in order to keep them cool.

Here are a few tips on how you could reduce computer noise:

- Use a computer case made out of steel rather than aluminum. Steel cases are thicker and they do a better job at masking computer noise.
- When purchasing a hard drive, check out if it has noise reduction systems. If it is possible, ask the seller to test a few drives for you and provide you with the most silent. There are huge differences between the noise level generated by different hard drive models, so this choice makes a difference.
- If you have a noisy hard drive, you can somewhat mask this noise by purchasing a hard drive mobile rack, and place your hard drive inside. The mobile rack significantly helps reducing the hard drive noise because the hard drive unit is no longer directly mounted on the case, and therefore its vibrations are not transmitted that well throughout the whole computer case. However be careful - better purchase good quality mobile racks because cheap ones are using cheap fans which in time may generate a lot of noise by themselves. In some cases, if the hard drive unit is not generating a lot of heat, you can even remove the mobile rack fan completely - but if you do that, make sure you do a test run for a lot of hours in a hot day and see if your hard drive does not overheat. In general, removing mobile rack fan can be risky for your hard drive life.
- If you have to choose amongst two devices that have different fan sizes, choose the bigger. Usually, bigger fans have lower speed for the same cooling effect (although this is not a rule) and also smaller fans tend to get defective easier than bigger ones (and when they do, they begin making a lot of noise).
- Always purchase ball bearing fans - they are usually more silent and much more reliable. Replace existing sleeve based fans on devices like video cards for example, with ball bearing fans.
- Use professional cooling systems which are designed for low noise where possible.
- Make sure your computer case only has holes in the back portion - in general those are enough to keep it cool if you use decent cooling fans inside. Holes in front area as well as on the left and right sides can significantly increase the noise leakage from within the computer case.
- Use fan speed regulators and set your cpu fan to the lowest speed that still allows proper cooling.
- Use additional low speed fans at the back of your computer and wherever possible, and then set the speed of your CPU fan to a lower level.

- There are lots of additional computer accessories sold today that can help a bit. For example there are plastic pads that can be mounted under fans and prevent vibration from getting transmitted to the case - and others like that. Get to a computer shop and ask the vendor for such accessories.

We have looked above into a few tips on how to reduce computer noise, that hopefully will be useful to you. As a general rule, using high quality low noise components and fans will be the way to go, especially if you spend a lot of time at computer. If you are planning to purchase a laptop computer, consider getting a low power consumptive, long battery lasting ones, like those using Centrino processors for example. These laptops are somewhat slower than the top ones but they generate much less heat and therefore less noise. If you do not intend to use the laptop for gaming or other cpu-demanding tasks, choosing such a laptop with low power consumption is a wise decision as it will not only work for more hours, but it will also generate much less noise than the more powerful ones.

My cats go ballistic when ever I turn on my Mac.
They start pacing up and down the house and start crying out loud meows non-stop. They just don't sit down and relax until I turn off the Mac.
Has anyone else experienced this with their pet?

I am intrigued! Our cat, 11 years old, can hear me spoon food into its bowl from outside the house 15 feet away, even when all doors and wondows are shut!

She is unaffected by my iMac - indeed often keeps me company by sleeping on my desk next to me (and the iMac) when I am working on something.

Were your cats previously owned by a windows user? 😉

Computers use switching power supplies. The transformers and inductors in the supply can generate noise so the switching frequency is set above 20KHz so humans won't hear it. Cats can hear higher frequencies. Of course it could be just that your cats think you are spending too much time at the computer, and neglecting them.

Try booting the cat on Dingo 1.0 and if that fails - reboot.