Check the fan for dust and debris. Over time dust can build up in the heatsink and may need compressed aired to clean out properly. Also check to make sure the fan power wires or fan shroud are not rubbing on the fan.
If everything is clean, and appears the be the fans themselves that have failed, , please register your graphics card and file a support ticket at https://support.xfxproducts.com/, in the ticket describe the issue in detail and also provide what troubleshooting steps you have taken.