I know this is strange. Some time ago, I bought a new 7200rpm HDD for my desktop system (I'll look for the model later). Every time the CPU is used, a high frequency cheep comes from the HDD. I'm sure it's the HDD because the problem does not occur if the HDD is not attached or is in energy-saving mode (I cross-checked by booting from a live CD). What could be the reason for the cheep sounds? Could it be the power supply?