Recently we experienced a power outage, and the PC was off. However, once the power came back, I switched on the PC and heard a strange noise - almost as if the hard disk or fans were struggling to work. I can't really describe the sound, but it's a laboured, loud sound almost like a jack-hammer. This has been persisting ever since the power outage, however the noise stops after around 10 minutes or so, and doesn't start again until the computer is turned off and on again.

At first I thought it had something to do with the HDD, but all my files are intact, chkdsk did not report any issues and performance is 100% unchanged, even in games (so the gfx card is fine, and so is the HDD most likely).

My PC setup basically has around 3 cooling fans, but I'm not sure if it's one of these either as the noise actually stops after 10 minutes or so, and if I leave the PC on for 4 hours (for example) the noise never starts again. It's there solely when turning on the PC.

I haven't got a UPS, and it's important to note that the computer was not on when the power went out - it was merely plugged in. I then promptly unplugged the PC once the power was out, and only plugged it in again when the power came back. Could it be the power supply? Unfortunately I can't open my tower as I would void the warranty.

Are there any tests which I could carry out without voiding the warranty?