My fans only make this sound at around 30% speeds so I don't hear it much. It almost sounds like wind howling. Below is a quick video (it's dark so you are looking at the top of the case) and at the very start you can hear the "howling...wwoooo woooo woooo," noise. It's a 1080ti sC2.

https://www.youtube.com/watch?v=04aVxMEUHyk

Update: After reading forums looks like it's common for the 10 series cards to make such noise due to style of fans: https://forums.evga.com/whistling-howling-noise-GTX1060-35-37-fan-speed-m2658076.aspx

Love the power of the 1080ti, but was so spoiled by the quietness of my good o'l 970 lol