Howdy you all,
Vehicle: I have a 2001 Dodge Ram 1500 5.9L V8 4x4 46RE
Issue: I have a knocking noise coming from the bell housing only after the truck has been sitting for 8+ hours. I used my stethoscope on the back of the engine to see if it was the rear rod bearing and I could hear the knock but when I put it to the bell housing it was a great deal louder than at the pan. I pulled the inspection cover off and inspected the flex plate. Found one bolt that was a bit loose. Tightened it to spec. Didn't hear the noise on start up but this morning started it up and hear it again. Most evident in the bell housing. Only lasts for a few minutes, no MIL lights. Engine oil pressure looks good and the knock does not go away once the engine oil pressure goes above 30psi. I did the plenum replacement last year, timing chain the year before that. Going to replace the oil pan gasket and 2 part rear main seal this weekend (rear main has been weeping for a while now). Trans oil and filter was replaced last summer.
i can hear the knock inside of the trans as well. I did recently switch from conventional to full synthetic engine oil recently.

Question: do torque converters knock? Any suggestions?

I am a 20yr heavy diesel tech, don't spend much time on gassers.

I will get a video in the morning or after work.

If the flexplate bolts are loose, torque converters can make some truly scary noises.

Flex plate bolts are torqued to spec, still makes the noise. Thanks though.

I wish I had helpful suggestions but please update if you figure this out.

If the threads are mashed it maybe "to speck" but still not holding the flexplate to the converter. Remove all the bolts and check the threads on them and the converter. Also see if you have lip on the flexplate where the bolt hole is.

I pull all 4 bolts out, applied blue loctite and retorqued them all to 35ft lbs. I inspected the threads and lips of the flex plate around the bolt holes but did not find any issues like metal on metal rubbing from loose bolts or cracking.
It knocked bad this morning when I first started it up but it went away after about 2min of idling. Still in the same spot... can be heard the best right at bell housing. Put stethoscope on the rear main seal area of the engine oil pan and could hear the dull knock, also put on bottom rear of the oil pan and couldn't hear knock at all. Put stethoscope on the bottom rear of engine block where oil pan and block meet, could hear a dull knock. Most evident on the bell housing. I am worried it may be a rod knock but don't know why it's more noisy and evident on the bell housing. Also noticed that under a load there is oil coming out of the bell housing weep hole at the trans dust cover. I know it isn't engine oil due to the rear mail being dry with the cover off. Though the oil has no scent as far as I can tell and also isn't very red. I have an appointment with a reputable trans shop on wednesday to figure it out.

So I pulled the oil pan, oil pump and rear main bearing cap. Replaced the rear main seal, oil pan gasket and oil/filter. Ran for 20min for oil to get hot to check for leaks. Knock is still on trans side but have more engine Rattle now. I rotated the crank when I was in there and neither saw nor heard any problems except for a bit of lateral movement on the rod caps on all of the rods (dont know if that is normal or not). Forgot to run cheap oil and filter in the engine after opening it up so going to get more oil and another filter with a can of Restore today. Knock is definitely in the bell housing still.

So, I forgot to mention that I recently switched over to full synthetic 10w-30 engine oil and the knock started right after that. I have read some articles and seen that this happens sometimes. Thinking of going back to half and half. Any opinions?

Might change it to some 10W40, and see if that matters. Dino or Synthetic is up to you.

So, did the oil change back to Castrol gtx synthetic blend 10w-30 and knock disappeared! It's the rear main bearing. So I need a new engine! Anyone recommend a good crate engine?

Thanks for all the help!