I opened my iMac's box a few hours ago - EXACTLY the same story as
Tjmckay4. In other words, I am upgrading from a 2011 i5 3,1 GHz and got the 2017 27" base model with a 512GB SSD.
I confirm that the fan is audible at 1200 rpm. Yes, as pointed out earlier, it is more the stream of air that is audible, it is not a real "fan" noise. Right now, I cannot hear it as the laundry is being cleaned downstairs. But when it is 100% quiet in the house, I can definitely hear the fan.
With my 2011 27", there is no difference in terms of fan noise between idle and the machine being shut down. It is 100% silent, unless I put stress on the CPU. I was expecting the same with the 2017 model, but I am a bit concerned that it is what it is and replacing it won't help.
Not sure what to do now...