My iMac 2.66ghz 20" 2009's CPU fan clicking?

Hi

Just the other day my iMac started making a ticking, clicking noise and through various pictures of the inside of these things I located the noise to the CPU fan.

Is this something that happens alot to these models?
I have fired the fan up to full RPM to see whether it was dust causing the issue but with no luck it still clicks.

Could there be a software issue thats doing it? I have repaired permissions and everything but no luck

My warranty has now expired because I stupidly didn't take out Applecare, im thinking of opening the thing up myself as im used to opening up macs.

I just want to check whether there is anything I can do before I open it to sort the problem and anymore info about it would be great

One thing I have noticed is I now don't think it is the CPU fan but the optical drive fan....

I have been firing the fans up with 'Fan Control' and CPU and Hard disk fans fire up fine, when i try the optical however it doesn't go above 1500 RPM??

I did notice it fires up when I control the CPU fan though and the noise disappears only to be replaced by a huge fan whirring sound (as expected).

Do the sensors in my iMac control both the CPU fan and optical drive fan together??

Apparently there are quite a few posts relating to fan noise for your model iMac. I just read through several of them. It seems the noise is (high speed RPM) is sensor related. Several articles suggest resetting the SMC first to see if the fan speeds return to normal.

You mention the CPU fan and then you say you have an optical drive fan. Are you sure that second fan is for the optical drive and not the hard drive?

Anyway, you probably should open the iMac up to see what's going on if the SMC reset doesn't work. Be careful opening up the machine and make sure you have the proper tools on hand first. You need glass suckers and a good set of torx drivers.

Cheers for your help

Yeah it is defo the optical drive fan as there are 3 in the machine.
I discovered this from looking at the ifixit guide.

There is a CPU fan, optical drive fan and a hard disk fan.

I shall grab some suckers and a torx set off ebay and give it a go opening it up.