try locking your frame rate to 60fps and re run games if the fan dosnt spin up to 100% try increasing the refresh rate until you get problems with gpu fan noise, once you've reached max refresh rate with no gpu fan reving that will sort the issue
Have you set up some kind of custom fan curve in the AMD drivers? I'd suggest uninstalling any third party graphics apps (like Afterburner or GPU Tweak) and resetting the Radeon Setting back to default to see what happens.
Both the AMD Radeon setting and GPU Tweak have settings for this, so I would not be surprised if they are interfering with each other.
I've never heard of a motherboard causing the GPU fans to spin up on a discrete GPU. The fans on the GPU are controlled by the GPU, nothing to do with the motherboard. The fans will only spin due to load/temp on the GPU, and any changes you've made in the utilities that control the GPU.
I'd suggest trying the board in another motherboard, but I think that would work and be misleading, as you'd also be running on a system that isn't misconfigured like yours is somewhere. You'd probably have to do a clean install on a spare hard drive to truly prove it's your setup and not the motherboard.
Have you updated the motherboard BIOS yet?