I have a 2007 C6 LS2 Bone stock with 137k miles. Started to notice a faint knocking noise upon acceleration and have no idea what it is. My Oil pressure however always runs a bit low, around 19psi fully warm at idle, never goes above 40psi fully warm. Th Knocking can only be heard in the cabin, not from the outside. Prev owner said it always knocked like that and he had gotten it checked out and couldnt find anything wrong with it. Oil pump going out causing the lifters to knock? and suggestions?