Here is my story with my 2015 rMBP 13 inch (2.9 GHz Intel Core i5, 8GB RAM, 500GB SATA):
I bought it recently (about 2-3 weeks ago) and soon noticed a clicking noise from the fan. The best I can describe it is that it emitted a sound similar to old home movie cameras (fast tick-tick-tick sound). The reason I knew it was the fan is because it was louder on the right side (this laptop only has one fan on the right side) and when I put the computer to sleep the ticking noise would decrease slowly until it stops.
I took it to the Genius bar and they told me that while they were inspecting the fan, it died on them! It would not even re-start at all. They were glad I brought in because otherwise the MacBook could have been damaged from excessive heat and I would not have noticed that the fan is not running. They ordered a new fan kit and confirmed that it is now working as designed.
Having this experience, I purchased TG Pro to keep an eye on the temperatures. The MacBook runs hot (idles at about 50C). When I startup the MacBook, it can go up to 105C because of nothing more than Dropbox or the Contacts app syncing! No gaming or otherwise. The fan does kick in, but it is really strange that when you simply start the MacBook to hear the fan going full bast trying to cool the laptop down when you have not even started doing anything.
I am thinking of bringing it back to the Apple Store for further diagnostics, but I can imagine they will tell me this is all normal and it is working as designed.
It could be that Dropbox and Contacts are buggy and needlessly stress the CPU. I will disable Dropbox and do more testing.
Any ideas or advice would be highly appreciated.