FE light tap & rattling noise

[DanEC]

I have a couple video files of engine noise but unfortunately they may not be clean enough to tell much. This is probably the most useful one.

[ame]https://www.youtube.com/watch?v=80q_sC9j8qM[/ame]

The car has under 300 miles on it and it has had a light tapping most of the time. I don't remember it when I first fired up the motor in the car but the header ceramic coating failed immediately and had to be re-done and I changed the break in oil out before starting it again. That is when I first remember hearing some light tapping noise. The car currently has 10W-30 oil in it and runs about 20 to 25 psi at hot idle.

The motor has a flat tappet hyraulic cam with adjustable rockers. Today I very carefully ran the preload settings "again" using the ICE/EOI process for each cylinder, using movement of the rocker and up/down on the pushrod to verify 0-lash, and then lashed them 3/4 more turn. All the lifters were still pumped up when I started the adjustments so I don't think it's a lifter that is stuck or not pumping up. When finished the noise may be a little slighter but it's still there.

I've been all over the motor with a stethescope, a long screw driver and a length of rubber hose and I can't isolate the noise anywhere. i've tried all along the valve covers, exhaust ports, intake, the fuel pump, etc. The noise does seem to be a little more to the passenger side of the engine.

When adjusting the lifters I did notice that the tin drain pieces on the driver side looked to be right against a couple of the springs so I bent them slightly away but that didn't appear to be the issue. Couldn't see anything else on the valve train that seemed out of place.

It actually seems a bit louder underneath or through the side vents as I tried to indicate in the one video where I stuck the camera down by the rocker. All that makes me wonder about an exhaust leak except for 2 things. One, I'm running SCE copper gaskets and two, when driving along with light engine load it will go through cycles of whirrling, rattling, racket - with the top on right now I really hear it. Step on the gas and it quiets down. I have undercar exhaust - I probably would have a harder time hearing it over side exhaust.

Motor runs good without issues. Plugs a bit sooty but dry. No issues otherwise. It's been nearly 35 years since the last motor I had with headers. Header always make some noise but I don't remember them sounding as thrashy as this. I've also had the headers loose and tightened back 2 or 3 times and wonder if the SCE gaskets just aren't sealing anymore. All my header slip joints were sealed with Walkers exhaust joint sealer. I figured the SCE gaskets would be good for several cycles of removal/replacement but maybe not??? Anybody had an issue with copper gaskets not re-sealing in reuse? Sound like an exhaust leak? Worth getting another set of those pricey gaskets?

Trying to eliminate all obvious ideas before turning to the builder.