Just putting it out there as someone may have come across this situation. I have a 66 Chevy II with a SBC 400 and a Muncie M21. As pf lately, there is a knocking noise when I start the car up. It is consistent during the entire warmup period. After it’s fully warmed up, it’s virtually non existent. When I first heard it, my stomach sank a bit as I immediately thought of a rod knock. Pulled the oil, not one spec of metal and being that it eventually settles in and quiets down after about 10 Minutes, my thoughts are the rod bearings are ok. Could it be a flywheel, could it be piston slap? What would cause a knocking noise then clear up after warmup? I own the car about 6 months and don’t remember hearing this noise until about a month ago. I will also say that when the car is hot, the Muncie transmission will grind when going in reverse. I’ve read that if I shift into second gear first, then into Reverse, that may help. Haven’t tried it yet as I drive the car about once a week. Thanks in advance for your thoughts.