My PC was getting pretty old, 5 years or so, and over the course of it's life I replaced the graphics card, HDD and a couple of sticks of RAM; but the PSU, processor, motherboard, fans etc. were all original.

A few weeks ago, I started hearing an odd noise. I struggle to describe it, it sounded sortof like the 'click of death' you hear when a HDD may fail, but not quite... (And it was far less irregular) Also, I was sure I heard it once or twice a minute or two after I shut down the PC. This was going on very irregularly for a couple weeks. Some days I would hear no noise at all, others I would hear it often, maybe once every 30 seconds or so. I could find no common denominator - i.e. it did not happen more during gaming or any other intensive use.

Anyway, I need my PC to sit some classes over the summer, so I put it in for them to run a HDD stress test and to replace a bunch of the components. I ended up replacing almost everything - the only elements I still have are my blu-ray drive and graphics card. They said when they started to run the HDD stress test it failed instantly (They started the test and it immediately said 'Test Complete' so they assumed it was at fault, and put a new HDD in since I was still under warranty with them.) I took it home a few hours ago, and I am still hearing the noise!!!

Do you guys have any theories?

I'm getting a little worried, I can't afford for my PC to suddenly fail during the next month - I have a lot of coursework to do. Any thoughts?

Is it possible it could be the fan on the graphics card?

I'm confused because it's so irregular. Any help would be much appreciated.