Sorry Ploki I would very strongly disagree that the fans coming on at random is hearsay. I have now been through 4 machines over the past 2 weeks all with the same issue. It has been driving me nuts as I exchanged a perfectly great 2012 rMBP that did not have any of the same problems faced with the 4 2013 rMBP.
There are some threads already here regarding this problem and several more on the apple support communities.
From my own tests over the 4 units and from others it seems to be a problem somewhere with the SSD.
The apple store took the stance of it's meant to do that at first. So explain why the 2012 did not? Then when presented with a video I took of the issue they agreed "it isn't quite normal". When my 4th unit failed the apple hardware test and sprung up a problem with the HDD/SATA they finally were convinced that "OK something is defiantly not correct."
They offered me another exchange but after going backwards and forwards from the apple store and exchanging unit after unit only to be deflated every time when the problem occurred yet again I opted for money back on gift card and I will wait for a little bit of time for apple to sort the problem out.
Fingers crossed
So 2013 rMBP has random fan bursts and 2012 does not? Man you were unlucky. I bought mine 3 weeks before 2013 got out and I gotta say it works flawlessly.