apple care replace hard drive

I've had my imac for 3 years now, everything hardware wise has been great other then when my super drive failed (3 months ago) but apple care gladly fixed that, also my applecare expires in december.

My roommate called and told me that there was some serious clicking sounds coming from the iMac. I told him to turn it off and that i would look at it when i was home. When i started the imac it took longer then normal to boot, but eventuially came to the desktop where about 5 minutes later it froze up on me. not something that happens reguarly or even at all on my computer. I turned it off and let it sit for a couple of days as i had other stuff to do.

yesterday i planned to make a local backup of my data; as soon as it booted up i closed all my "open at login apps" and started with doing my backup. I left the computer on over night to transfer the data through the network and so far the computer hasnt given me any trouble, no clicks (i can hear the hard drive seeking and what not), no crash reports, nothing at all.

even with the imac running fine the last 12 hours im still worried that the hard drive will go out soon. is there a way to check on its status? i do see something saying its S.M.A.R.T verified in the System Profiler.

If I had another hard drive and brought it in with my iMac would they be able to switch the two for me? or maybe a small service fee? or is there a way to show my hard drive might fail?

thanks for your time,