I am having the same issue. I have found that this happens when you write a large amount of data to the SSD drive. For example, when updating software or downloading large files. From what I've noticed so far, this happens with about all early 2013 Retina MacBook Pro's, no the older versions. The temperature is just fine, so I hope this can be solved with a (firmware) update.
No you are wrong, I can confirm that my 15" MacBook Pro Retina Display with 2.3GHz Core i7 processor / 8GB RAM / 256GB SSD (made by SanDisk) is indeed having this same issues with the fan, is very annoying !. I bought this machine on December 2012 and it has a Samsung screen (not LG) if it matters.
Most of the time the fan kicks start up to full speed even just surfing the web with only a couple of tabs open and no other applications running at all, the machine itself is actually cold (not even warm) to the touch of the hand.
I really hope this is software related so Apple could fix it with a new firmware update. So Apple please fix it asap !