There's no golden bullet. If you can guarantee a constant level of power delivery you can tune your circuits to minimise driving frequencies in the audible range, but that doesn't work for modern GPUs that use aggressive voltage shifting and segmented power gating. Using more coils to spread the load adds cost (of both the coils, and the extra copies of other components needed to drive them) and board size. Other DC-DC conversion methods either are far too bulky, too inefficient (It's no good having a 150W output if it requires an 1800W input and dumps an extra 1650W of heat into the case), or both (as well as being expensive).
It may be more viable to use mechanical fixes, like using potted encapsulated inductors and placing these in a soundproofed enclosure, but this adds extra bulk, extra cost, and could cause thermal issues.
Switching to lower distribution voltages inside the case (e.g. 3V rather than 12V) would reduce the noise due to the smaller step-down, but would dramatically reduce the maximum cable length (OK for ITX, no good for a regular PC), require much thicker gauge wires, and would not be compatible with current ATX specifications.
It may be more viable to use mechanical fixes, like using potted encapsulated inductors and placing these in a soundproofed enclosure, but this adds extra bulk, extra cost, and could cause thermal issues.
Switching to lower distribution voltages inside the case (e.g. 3V rather than 12V) would reduce the noise due to the smaller step-down, but would dramatically reduce the maximum cable length (OK for ITX, no good for a regular PC), require much thicker gauge wires, and would not be compatible with current ATX specifications.
