I upgraded my computer last night, replacing almost everything and installing a CoolerMaster Silent Pro 600W. All seemed well, when just randomly browsing the internet, my computer made a loud crackling noise. It sounded electrical and didn't seem to be coming from the speaker, so I thought it was the PSU (even though this particular brand is not known to have problems.)
With the power off I inspected my PC with a flashlight. I could find no evidence of capacitor wear or damage of any kind on either my motherboard, or from inside the PSU (from what I could tell.) I booted my PC back up and checked the voltages and temperatures (both in the BIOS and with SiSoft,) and everything seemed normal.
So then I ran SiSoft's burn-in benchmark suite for a good hour. Nothing, no warnings, no instability. Then I played Starcraft 2 with all settings on Ultra for a good hour. No sounds, no instability, nothing out of the ordinary.
I never heard the sound again after that. Is it possible a blob of dust got lodged somewhere and touched a component it shouldn't have? I did notice that the cable for a chassis fan was stuck under my motherboard something good, I had to tug a little to get it unstuck. There was a slight scratch on the cable from that, but certainly no burn marks. Could that have caused the noise? How worried should I be?
It could be a sign of a bad capacitor on its way out within the PSU itself. You didn't smell a electrical based burning/smoke did you? However, as long as everything is working fine, I would just keep an eye on it to make sure. If it makes you nervous, I'd get in touch with CoolerMaster and see what they have to say. They may send you a replacement to be sure.