I have a loaded Aurora-R6 (Intel-i7, GTX-1070, etc.). With 850w PS and Liquid-Cooler of course.
I would not call it silent. I'm not sure its even possible to build a silent high-performance desktop computer (at least not affordably).
At idle (or even surfing web, or writing a document), the Aurora-R6 is pretty quiet. When gaming (Fallout-4 or WoW) the fans pick-up (they have to or something might melt-down).
I've seen some tiny HTPC that are pretty quiet, but they are custom-builds and were really only built to (just barely) decode 1080p video and HD-Audio in Home Theater environment.
We just installed some Dell OptiPlex 5050 SFF (as a favor to a client). Those are small, quiet, and very fast (Intel-i5, M.2-SSD, on-board Intel graphics only).