The flywheel on automatic transmission engines are called flex plates. Because they do flex.
I replied a few post up a week or so ago to check the vacuum line for the transmission. I had zip tied mine to the filler tube because for the last 3 months every now and then. I would get a metalic ping when starting from a stop and hitting the fuel enough to pull out in traffic. It wasn't every time, just normally from a stop to high torque applied.
I was convinced the problem was related to the belts, pulleys or cooling fan since it sounded like it was from the front of the engine and the ends of the fan blades had gotten scrapped up sometime in the past 25 years. I just lived with it.
Monday, my starter died. I installed the rebuild last night. This was my first time pulling the splash gaurd under the flex plate for this truck. Everything looked fine and from reading things on here. I put a wrench on the 3 converter bolts on the bottom. All 3 were tight, the flywheel had no cracks and the rear main seal while moist, wasn't really wet. I left the heat sheild for the starter on and put everything back together last night. Fired it up with the cover off and no noises, great increase is starting speed. My starter had burned up the brushes, worn out all 3 bushings and was needing help.
I buttoned everything back up, loaded up Colton and the dog for a test drive. I love the new starter firing the engine up before I can think to turn off the key. Put it in gear and we had a constant knock. Put it back in park and the noise was gone. I put on the parking brake, had Colton hold the service brake and put it in gear. I crawled under neath and isolated the splash gaurd for the flex plate. Everything got turned off, I loosened the 6 bolts, moved the gaurd around some and tightened them back up. Noise gone.
We went for a drive and the noise came back anytime I pushed the throttle at any speed. I don't fancy burning my elbows, so I parked it last night, came inside and got on SS. Searched for threads like this and narrowed it down to the heat shield for the starter or a bent splash gaurd.
I went out this morning to pull the splash gaurd and look at the heat shield. When the splash gaurd came down, a nice circular shiny wear mark was evident. Back to the wrench on the converter bolts. 5 were tight. The 6th was about 2 full turns loose. Got it tight, buttoned everything back up and the noise is gone. Just drove the truck in town and on the highway for about 20 miles. No noise.
I know I wrote a lot to tell you to check the converter to flex plate bolts. However, I did check them. 3 of them. Check all 6 and look for cracks on the flexplate.
That M1009 is excellent on fuel mileage as well. Nice rig, we enjoy it! Glen