The squealing you hear is most likely as others have mentioned is capacitor/coil whine. This is caused by oscillating action in the currents/voltages.
The cause of this noise/fluctuations are hard to pin down, as they could be from various sources, the PSU, the card, other devices, EMI, mains.
High frame rates often cause sequel, as higher frequencies/refresh rates are passed through the card/PSU increasing the tendency for the unwanted high frequency noise to make the capacitors/coils vibrate in such a manner.
Very often inside PSU's it looks like someone has had a accident with a glue gun. With huge splodges of glue on top of capacitors/coils. I suspect that the reason for this is to dampen the noise generated by these vibrations as well as to electrically insulate the components.
See for example this image of a reasonably respected psu.. "Glue" has been dropped on/around the capacitors/coils.
My understanding is that is not necessarily a sign of poor quality components or a sloppy psu build, the glue is there intentionally to reduce the negative side effects of how components/electricity interact with each other and the resulting effects.
Sometimes a PSU can cause the components on the gfx card to whine, sometimes the gfx card can cause the components of the PSU to whine, sometimes even the motherboard/cpu or dvd drive could have an effect on another component.
Often the part making the noise is not the cause.
So what can you do.. It maybe easier/cheaper to not worry about the cause and try and fix the issue. the end result is the same, no/less noise.
1) Try and filter out these unwanted frequencies that cause the problems using filtered PCI-X/Power cables. Even noise from the mains electricity could be passed on. Some "kettle leads" have these filters, or maybe a UPS/filtered power-strip may help.
2) Locate the "whining component" and slap some "glue" or I have heard people using nail varnish to stop it vibrating. A paper tube held to the ear is a good way to pin point which part is making the noise. (only issue here is that doing so "may" invalidate warranty..
3) It is entirely possible the card or PSU or even another component is just not up to scratch, and replacing it may solve the issue. Or it may just have different tolerances with the other components in the system.. A squealing card/psu won't necessarily behave in the same way when used by another person/system. I'd expect some PSU's have varying tolerances to this, however from experience just because they are high end, has not shown them to be more or less susceptible.
4) Some people can't hear the high frequencies, as we get older this range of high pitch noises should become less of a problem.. try waiting 10+ years.
5) I am no expert, all posted is just from observations. I have little knowledge of the internals of PSU's or capacitors/coils.. The technical terms I have used are no doubt wrong, the meaning however should not be , having had encountered this problem so many times, the above is just my findings.
