My HUD flickers too cause i use dual GPUs (at least it did when using DisplayPort), i had to wait till i joined a server or a SP game and the flickering started then i went to advanced graphics options and changed any one of those and went back in game and the flickering was gone.
Ive been troubleshooting for about an hour before posting here though. high with DX11 and high textures, Ultra with DX11 and high textures, high textures only, etc.
Any graphics settings where DX11 was active, I got flickering. if I turn off DX11, but leave everything else on Ultra, I wont get flickering, but then I wont have DX11.
I am using two AMD radeon HD 7970's