I have a rattly knock at idle and up to about 2k rpm. I inspected the flex plate, tightened the bolts on it because they where a bit loose. Found no cracks on it either. I changed the oil and it looked normal, no metallic flakes in it and no coolant mixes in either.. Other than the sound it runs perfect, much as a check engine light or anything. It sounds like its coming from toward the back of the engine down real low.
Its faint in this video, but you can hear it.

http://static.photobucket.com/player...pse692e265.mp4

 

Does it go away when it warms up? mine has a rattly knock when I start it takes till the oil pressure is up to start but once its warm the rattly knock is almost gone. Mine runs great also. Im gonna drive her till she blows. a can of RESTORE shuts her up for about 2 weeks at most.

 

No, it stays the same pretty much all the time. It quiets a little bit after its warm, but it still makes the noise. It almost sounds like a diesel at idle.

 

Mine doesnt disappear it just quiets significantly. OIL PRESSURE is good correct? I really dont know what mine is. mine has done it since i bought it about 15000 miles ago.

 

Updated with a video... to help with diagnosis.

 

mine sounds like a diesel too but only at idle, the oil pressure drops, im gonna do the rod bearings soon, that should fix it

 

I bought a mechanical oil pressure gauge today, will post up results tomorrow. I really dont know what is going on. Hopefully the oil pressure readings are healthy. It only turned over to 110k miles today.