Hi guys, I am hearing a knock or rattle coming from my engine. Sounds like a loose rocker arm, and you can really hear it from the driverside floor when the windows are up. I bought a mechanics stethoscope, and have narrowed a noise that sounds like something is loose, to the top end of the engine. its much louder on top anyway. but I cant narrow it to either bank of the motor. I listened on each exhaust manifold port and the noise is present on all cylinders.

other info:
Noise is louder when cold, but still there when hot. noise is loudest when maintaining a steady cruise at 50-60mph, and quites down on mid to heavy acceleration. You cant hear it at all on decel, but it comes back when the injectors start firing again at close to idle. The truck runs fantastic, starts fine hot or cold, plenty of power, no smoke, no miss or stutter, and no puking! (at least I fixed one problem haha)

history:
Noise started 300 miles after I changed the head gaskets with ARP studs and EGR delete. At that time I also replaced: Fuel pressure spring, standpipes, dummy plugs, MC filters, shell T6 oil, and installed a turbo back 4" exhaust. Had the heads checked for cracks and resurfaced, they took .007" off to get them flat. Also replaced a few hundred miles before the HGs were the IPR valve, Oil cooler, and fuel pump.

So far I have checked:
Exhaust hitting fire wall.
Inspected drivers side rocker arms. They were all still in place, but I didn't remove them. Also re-torqued the injector hold down bolts.
Drained fuel/water sep thinking I had some bad fuel. also used 2 stroke oil in fuel, which didn't help much.
turbo v-band clamps tight
up pipe bolts tight
drivers exhaust manifold bolts tight

here's some video of the truck.

First is a cold start the second is inside the cab at operating temps.

thanks guys. I hope this isnt something major.

YouTube - F350 Cold start 60*F

YouTube - VID 20101107 180149