1990 YJ. This one might be an expensive fix, or not. Sounds like a high pitched muffler rattle but, I know it's not. Sounds like the flex plate is loose but, it's not. Jamming a thick washer between the crossover exhaust pipe and the bell housing makes it stop. I hear this noise under a load in first or second gear. Engine is the 258 AMC with an automatic. My left knee doesn't let my drive a manual tranny anymore. The rest of me is in bad enough shape that I have to hire others to twist my wrenches. Without a recording of the noise, anyone want to stab at it?