My PC starts making a strange buzzing sound after being on for ~15 minutes, regardless of what is happening (no intense gaming or processing) and the CPU temp seems to remain normal. I tried looking up coil whine but didn't seem to explain what I am hearing. I also used an aircan on the fans and that didn't seem to do anything.
The sound goes away immediately when the PC is turned off. The noise seems to come from the top of the PC near the power switch. Any idea what is causing this sound and how to fix it?