Hello all I am starting to have an issue with my 350 SBC that literally just started today. It all started when I pulled over at a gas station after driving 30 minutes on the freeway to fill up. After starting the truck, I heard a loud knocking noise that went away after about 30 seconds or so. I noticed that the noise seemed to be coming from the driver side of the motor. I also noticed that the sound was loudest if I stood where in between the cab and the bed of my truck. Anyway, I pulled the driver side valve cover and checked the pushrods by twisting them with my index and thumb and some of them were loose. After tightening them up, I started the truck again and the problem went away. However, on my way home I stopped by a relative's house and after getting back in my truck and starting it, the sound came back. Except this time it lasted longer but eventually went away. I don't hear it while I'm driving only when I've shut the motor off and let it sit for probably 10 minutes and start it up again. Does anyone know what it might be?