I am having an issue with my Sig P239 Tactical 9mm. It is a Gen 2 with a DAK trigger. In DA mode as I pull the trigger back slowly I feel a slight grinding/stuttering in the trigger. My best friend has the exact same weapon and says he experiences the same thing. Can anyone shed some light on it. Seems like this would not be happening in this weapon. I have tried lubing everything I can, but the issue persists.