Compared to other all-in-ones that I've used, I think Apple is doing the best when it comes to fan noises overall on all of the Mac computer line up. I could only imagine how loud will iMac Pro will be since it's talking about multiple fan blades and 70% better cooling capacity, despite Apple's statement which says it will run just as quiet. We will just have to see, but on my 2017 iMac I measured at around equal fan noise compare to my outgoing 2015 27inch iMac, both core i5.