There are no movable parts inside a CPU, so there's no way the chip itself can generate any kind of noise.
There are, however, a number of switch-mode power regulators inside the PC, and these can produce a high-frequency hissing noise under certain conditions. The PSU contains a few of these regulators, and the other(s) is/are found on the motherboard, in close proximity to the CPU.
When a noise like the one you describe is being emanated from a switch-mode regulator, is usually means the circuit is overloaded or defective. A low-amplitude, continuous, constant-frequency high-piched whine is not uncommon (and not necessarily an indication that something is wrong), but this sounds more like white noise where the frequency is constantly shifting. If you're correct about the sound coming from somewhere near the CPU, it could be due to a bad capacitor on the motherboard. Look for
leaks or signs of
bulging.
Better power management could be the reason you're not hearing this sound when you're running Windows 7. Try running a demanding game or a CPU benchmark, and chances are you'll hear the same sound.
