I built my computer around 2 years ago, and at christmas I bought a new PSU, Hard Drive, and some RAM. Just yesterday when I turned the pc on it made a very dodgy sound, and when I opened it up I could hear it was either from the PSU or CPU, though I'm not sure which. I turned the computer off straight away and have tried turning it on several times since and I still get this same noise. I'm a bit of newbie when it comes to hardware problems; is it safe to just let my computer boot as normal even though there's the odd sound? And does anyone have any ideas on what it could be? It sounds like it might be a fan noise.