What is this noise?

[SoNic67]

http://www.youtube.com/watch?v=61CSLc6hV4Q
For a while I was suspecting that I have low oil pressure.
Tonight I did change the oil to 20W50 and the pressure at idle-warm is higher - 15PSI.

The strange noise still persists. Weird thing is that when I coast without stepping on gas, it is that loud. When I touch a little the gas pedal, the noise disapears. There is no visible change in RPM's or oil pressure, just the engine starting to "pull" the transmission, instead beeing "pushed" by it.

Can it be something else? The timing chain slack? What else can "shift" inside the engine with the load?

 

[windsors03cobra]

Probably valve train noise from not having any oil pressure, probably some rod and main bearing clatter mixed in for good measure. No oil pressure due to a wiped out rotating assembly. No saving it either save for a full rebuild.
In short your motor is saying "Goodbye". Junkyard motor it man, find a good one for 500 or so and have it put it for another $500 or so.
Looks like its worth it. I have the same truck with 203k on it and I would put a motor or tranny in it.

 

[SoNic67]

Thanks for answer. Yep, I guess rod bearing sounds right - connected with the load.