1999 Ram 3500 5.9 Cummins 24v 2WD 5 Speed

So I have this knocking noise and this is my first diesel truck. I'm fairly mechanically inclined but not so much on diesel motors. I've developed this knocking noise. Sounds like it may be coming from the rear of the motor. I feel as if I can hear it more prominently when I bend down and listen under the truck. Now my first thought was rod knock but I'm not so sure. I've been running it with this sound for about a month now and it has just recently gotten louder. I know your probably cringing at me saying that but here's why I have driven it so long. At first it just sounded like excessive valvetrain noise so I planned to adjust the valve lash but didn't have the experience in doing so or the feeler gauges. So once I did enough research on the proper way to adjust them and acquired the gauges, I adjusted them and it still didn't fix the sound. I've continued to drive it to see if any other symptoms would arise. So far I haven't noticed anything like white smoke, loss of power, or low oil pressure. Only issues I've seen is the noise itself and an RPM fluctuation of 50 RPMs. Other than that the truck runs great and does not miss at all. So just to ease my mind I figured since I've drove for over a month with this noise, if it was a rod knock, surely id have some kind of metal in the oil. Just checked tonight and no signs of metal shavings in the oil. Not even the glittery shimmer of very fine particles. As far as I can tell it isn't a rod knock or injector issue and its not valvetrain noise. I'm stumped at this point. Any ideas?

I believe the video attachments aren't playing the audio so here is a YouTube link to one of the videos.