G5 making clicking sound

It just started doing this a couple of days ago. Every ten minutes or so, while the computer is on, I'll hear this weird sound. It's the sound that it makes when you put the computer to sleep, and it sounds like a fan engaging or disengaging, or something. Has this happened to anyone else? Is it normal? Should I be worried?

What are you working on while doing this?

I believe it does this when it's working hard at something, or doing multiple heavy processes.

Just on the internet. Nothing out of the ordinary...

Sounds like a hard drive issue. I had the same problem and my hard drive ended up failing. I would definitely get it looked at before you have a major problem.

I have TechTool Pro 4 and I just started the Advanced Suite test thingy. So if there is a problem, this should find it.

Does it, slow down? lock up or freeze? I had to return a G5 for this and it was making a noise from the Fan (which i thought was normal)
The fan would be on low idle then kick in hard for a sec then back to idle then after a while it started to slow and freeze up sometimes, when before it ran fine??

Well, TechTool didn't find anything majorly wrong. There aren't really any performance issues. I'll be comfortable just knowing that it's not a hard drive issue.