iMac 27" clicking

In the last week my 27" iMac, bought maybe 15 months ago, has started making a clicking noise.

I found a You Tube video which illustrates the exact same noise, but the person who posted it doesn't tell what the answer turned out to be.

Anyone heard this before? - Clicking imac - YouTube
Many thanks
Stephen

That's the hard drive clicking..you should be hearing a little bit of it during normal operation, but if it starts to follow a pattern like in the video there, you might be nearing HDD failure..

You should make sure you have a good backup of all of your documents..

Start up Disk Utility and check the S.M.A.R.T status of your HDD to see what it says..

thank you! ... as well I bought the three year warranty