One of my molex fans was doing something such in the beginning and after the noice got louder and a little luft got visible, I got pissed off and threw it away.
My gtx 1060 had a noicy fan as well while also with a bit luft, though it was a little different sound there. I simply latched 2x 12 cm fans instead and it is also running cooler than with stock fans while also with fdb bearing & high quality. Well, I was going to put them in the case one way or another
If it is not too difficult for you, you can remove the current GPU fans and connect one 120-mm or 90-mm fan to your mobo/molex and latch it to the heatsink of your gpu, closest/centered to the chip's location (check temperatures with MSI Afterburner or similar, at least in the beginning). And if the sound disappears, the fans are clearly the reason. (later on can put 2-3 fans if you decide and if there is enough space and connections, preferrably set 2+ ones working on 50% power via bios on 3- or 4-pin connection to motherboard). This little pciE slot nearby seems covered and unused anyway.
90-mm fans may actually be a better idea as three ones mb fit there more easily, but depends on connections, and via molex percentage of power can be regulated only with controllers.