This is because it uses CPU time when scrolling therefore making the CPU do work which makes it hotter and takes power from the power supply. The power supply fan simple speeds up to compensate cool the inners down. Try it, hold the X at the top of a window (if you have XP, on the normal settings - not classic) and listen to the power supply fan speed up.

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Say what??????????????????????

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Dude, Dont worry about the sound. It's a machine, they make noise some more than others. What you describe sounds real strange. I'd have to say the fan in the power supply but who knows if it goes out replace it. You do not need 400 watts. 300 in plenty.

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Sounds like electrical resonance to me The PS/2 Port delivers and receives voltage to attached peripherals. When you scroll up, you are sending a large amount of instruction sets of input (as the wheel rotates, it cuts a light path which then translates for the cursor to ascend or descend a predefined number of pixels.) This current creates a magnetic filed as it travels from the mouse to the port to the chip set, etc… The field interferes constructively with the wires in your power supply or the junction where it connects with the board or at some other adjacent point; the electrical resonance is then changed harmonically to acoustic resonance. The wires may be coupled to rigid shapes that oscillate with the same period of electrical oscillations. This is my brief theory. I don’t think you need to worry – I have seen the same problem with sound cards and wheel mice. In the past it was just assumed to be IRQ conflicting with ACPI – but there are other theories.

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