Ford F150 - Engine Grind

Hey all, I have a semi serious question about my truck engine. I have a 4.0L v6 and after a weekend of not driving the truck, I go to start my engine and notice a bad grinding sound coming from the engine, either the CAM or the Valvetrain. I check my oil on a regual basis and is always full. Why does my engine sound like it grinds on a cold start after sitting for a while? Is there something different I should be doing..? I have heard in other cases some engines dont have a large enough oil port from the pump to the cam/valvetrain...is that the case with my engine or something else?