I bought a '99 Ram w/ 5.2 a few weeks ago that had a slight knock. I was hoping it was the tensioner for the drive belt but I checked it out and that's not it. I've also read in the threads that the oil pump can cause a knock. This is a solid knock but not too loud. It seems to be loudest when I have my probe touching the block. It doesn't get louder as rpm's increase, just faster. In fact, I don't hear it much over idle but that may just be the fan noise covering it up.
One odd thing is that I changed spark plugs yesterday and then made a 45 mile round trip. It didn't knock at all after the first start and I stopped 3-4 times on my trip and never did hear it knock. This (cold) morning I started it and still no noise but when I got to work it's knocking again.
Any thoughts, guys?

 

What's your oil pressure look like? Can you post a vid, with audio?

 

Going by the dash gauge... at idle it's about 30lbs and driving rpm it's about 70lbs. I did notice that it takes about 2-3 seconds to show any pressure after start up even though I drove it less than 30 minutes ago. I probably need to get a good oil filter on it.
As far as video, I tried it earlier and all I could hear was other noises.

 

If it's lower end, it is either a rod, or main bearing..... it could possibly be valve train noise too though..... I would poke around a bit more, and see if you can definitely isolate where it is coming from. Lots of stuff can tap/knock on the motor.... even the engine mounts.

 

Truthfully, I was thinking main bearing (and may still be) but it's odd the noise went away after the plug change. Even after it was warm, nothing.
Well, it'll be a big problem or it won't. :-) I'll just keep checking once I have more time.