Found two visual bugs with the Fulmin. First one is that when using the Oberon Noble Animation set, while in auto mode your Warframe's arm clips through the gun.
The second one also concerns the Oberon Noble Animation set and auto mode. When standing still your Warframe will do an animation where he'll lean the gun on his shoulder, if you start walking during this animation the unique way the Fulmin is held during auto mode screws up and reverts to how other rifles are held, causing the silencer to clip through the gun as it's still attached to your left hand. This will then remain this way until you let the animation play again and don't interrupt it.