Computer making clicking noise

Hi, wasn't really sure where to post this, but I think this forum seems to fit the bill.

Ok, so the problem is that, as the title says, my computer is making a clicking sound. My computer is a desktop windows Vista, if any more info is needed, I'll give it.

The sound definitely isn't come from the hard drive because the sound is coming too far away from it. When I tried putting my head around the back on the computer, it seems to be coming from somewhere around there, maybe where the power cable is plugged in, but I'm not sure.
It doesn't constantly click, it seems random, it usually clicks for about 3-15 seconds each time, it is fairly quiet (you can't hear it at all if I'm playing music for example, unless the volume is very low) and the clicking is pretty fast. It will randomly happen every 30 secs-5 mins.

I have had clicking come from the computer before, but it seems to have been happening a lot more in the past week and I'm just a bit concerned. I have two fans on my computer, a small one at the front and huge one on the side and I think it may have something to do with the side fan, like maybe some foreign material has got stuck in there...? Both fans are still running absolutely fine however.

I am no expert with computers so I have no idea how to take them apart, etc. And I would be far too worried that I may break something in the process, lol.

Any help would be appreciated; I may take my computer to a tech shop to get it looked at since it I think it would be much easier to see what is wrong with the computer if it's seen in person. However, I never seem to find enough time to do these things and the nearest computer tech shop is a 30 minute drive to.

 

Clicking is never a good sound as that's a bearing starting to go, be it a fan or a harddrive. You can use an empty paper towel tube as a stethoscope and localize the area and not just guess at the affected component. Quite the cost difference between a decent power supply and a fan.

 

I just tried out what you suggested and it does seem to be coming from the power supply, though I must admit that I am still not 100% sure, but it is definitely coming from around that area.