Help me figure out this noise (please)

Well 40 miles till my jeep rolls over to 200k and it's starting to make a knock when I start it. At first I freaked out but then stopped and though about it for awhile, there is a loud knock when I start the engine, then at idle with no load it's alot more quiet and irregular, it doesn't follow the rpm's but will knock every once in awhile if applying the gas abruplty it will give alittle quick knock.

Normally I will get a diesel like noise at idle, which I figured thats the nature of the 4.0 with high milage. Then I got a faint clacking metal like noise at idle that also did not rise with the RPM's. I'm uploading a video just as a refrence for the knocking sound. I'm getting good oil pressure, the engine runs smooth and strong, in the rpms I'm not getting any unusal noises. From searching I gathered it could be.

Engine in the bottom end doh
The Water pump
The Flex plate
the harmonic dampner hitting the timing cover
or the timing chain.

What do you think?

Here's the vid
http://www.youtube.com/watch?v=dd1iaqjrdrw

Motor mount or some other loose mounting bolt? Doesn't sound internal to the engine. Could be wrong though, it's hard to tell without actually being there.

Does sound sorta like my flexplate did.
If it starts to follow the engine, gets louder at first at idle, goes away with load, I would guess that. Mine also made the same sound as in your video when shutting off the engine.

Sounds like your talking about Piston slap. this is a normal condition for an engin with that amount of milage. It's probably a list of other things that are loose and warn in the engin also. If you have good oil pressure and the engin isn't loosing any oil drive it till it blows up. My engin makes the same noise, worse when cold, it's been doing this for about 3 years.

The intial knock isn't piston slap, piston slap is more faint, I do have it but this is diffrent. Piston slap usually last for a minute or so after you start the engine normally.

After watching your video a few more times, the very first noise heard after the engin fires is not piston slap. You could try laying under the jeep and have someone start it (with out runnung you over) you may be able to pinpoint it that way. I have a stethescope (sp?) with a metal rod on it and you can put it on the engin or trans and hear what sound is coming from different areas. I got it at an auto parts store for like $10 bucks or you can do the same thing with a screwdriver with the handle stuck in your ear.