synapse1278

synapse1278, 6 months ago

I suppose, when you plug the HDD to the computer, it spins up and start drawing more current from the power-supply and the noise disapears. This is because the PSU has a buck-converter, the switching frequency increase proportionally with the current drawn by the load. When the current it almost 0mA, the switching frequency can be audible (electromagnetic forces can make some components vibrate, e.g: coils). When the current is nominal, the frequency will be ultrasound and you won’t hear it. I have observed this with many electronic devices. If you are worried, you can try another power-supply, after checking it has the same voltage and polarity on the plug, and can deliver at least as much current as the original one.