I parked my truck last night and all was good with the world. Got in it just now and tri to start it, it turned over then clicked. I checked the battery cables...loose, so I tightened. The truck then started and is now knocking in the drivers side. Checked oil, its fine. What could cause this sudden knocking? Possibly the oil pump?
hard to say without actually hearing the noise. You might want to have a shop listen to the noise and ask if they might know what it could be. As far as oil pump, is the oil light on? do you have an oil pressure gauge? it could also be a lifter that isn't pumped up. could be an exhaust manifold leak. could be a loose spark plug.
where does the noise sound like it's coming from? If it not a loud knocking noise (like a crank or rod bearing) drive until the engine is up to normal operating temp and shut the engine off. Let it cool all the way back down and then see it the noise goes away on a new restart.