brazil
I had a similar problem, removed the cover from the motherboard and dropped oil on the fan axis and the noise disappeared
Which screw(s) did you remove in order to get at the fan to do this? There's a small screw on the shroud near the fan and it looks like there might be someone on the back of the board holding it on as well (I really don't want to unmount my MB if possible if I can remove a screw from the front).
Like the OP, the noise is driving me crazy as well with my x299 Dark MB.