iMac Late 2012 27'' ticking sounds

I received my new iMac 27" last week.

After leaving the Mac with display sleep for a while and when I start working on it again, I hear these ticking noises on the bottom of the front panel. It goes away after about 5-10 minutes working.
This seems to be coming from expansion of the screen or body by the warmth of the LCD.

Does anyone else have any experience with this? Ever heard of this?