Is there an easy way to differentiate the two? Doesn't sound valvetrain related because it seems to be coming from the lower end of the drivers side. The original owner of the truck installed Kooks LT's so I figured there is really only 2 things it could be. Internal engine failure is starting (rod bearing possibly) or the gasket is leaking making it sound like rod knock. Only time you can really hear it is in drive-through's (sound bouncing off the walls) or when you get down near the drivers side tire. Will get a sound cilp up tomorrow when I get back to the house.....