OK for all you diagnosticians out there here's what I have. I'm the original owner 1999 F350, 7.3 Powerstroke, 4R100 trans, crew cab dually, 4wd, 313K miles. I just rebuilt the original transmission (big shout out to ATSG manual, and TransmissionBench videos) and so far so good, have about 750 miles on the new rebuild and it is working splendidly. My ear is very sensitive to any different noises at this time and here are the symptoms. A tapping noise has developed from idle to about 1400 rpm where it then disappears. It only starts after everything is good and warmed up, never when cold. It is not always there, sometimes you hear it sometimes you don't even when the driveline is warm. As I mentioned earlier, never when it is cold. It is definitely front of the trans, back of the engine area. You can hear it from outside but interestingly it is easier to notice from the inside with most of the normal extraneous noise suppressed. I don't think it's hard or loud enough to be considered a "knock" but is certainly more than a "tick". I remember the original torque converter developed a very loud "rattle" at idle that would go away as soon as any rpm was introduced, this is definitely a bit different. Some previous internet research suggests that the flex plate may be starting to crack, stupidly I did not thoroughly inspect it before putting the transmission back in. I do not think it is the torque converter although possible, it was just rebuilt and upgraded from the stock dual disc to a triple disc. The oil pump checked out very good during the rebuild. Last little bit of info, while taking out the transmission I noticed that a bolt had worked loose on the starter motor, I have never removed the starter since I purchased the truck brand new. In fact all three starter bolts were loose, I retorqued them all to spec. May or may not have something to do with figuring this out, I just thought it was an interesting point to add. Sorry this was post was so long, I just wanted to make sure I gave as much information as I could. If you stayed with me here, what are your thoughts and ideas? If you want more information, ask away, I'll answer all questions to the best of my ability.