Jump-start the PSU (
How To: Jump Start A Power Supply (PSU) / Test A Power Supply And Components) to find out if the whine is coming solely from the PSU. If it is, then try stopping the fan momentarily to see if it's the fan, or an electronic whine. If the whine stops, you could be looking at the motherboard, or an interaction between the motherboard and the fan. Separate the two and use your ears.