OK, this continues to drive me crazy, need your ears, it won't be easy

[My427stang]

Let's not demote him!  He was up for O-5 last I heard, and that is worth at least two Captains!   On the noise, I had a CJ from the factory that had rod inserts that looked like they were beaten in with a ballpeen hammer.  Warrantied at less than 3000 miles, and the reason for the warranty was a noise off idle and with no load that only I seemed to be able to hear at the time.  The service manager did think he heard something, so they took a look.  Long story short was I got a rebuild and the car was super quick afterwards and no noise.   Joe-JDC

Thanks Joe, I'll keep looking.  BTW, the USAF must have been desperate because they put eagles on my shoulders in September.  The good guys must have all got out at 20   I am at 22 years this year and have at least 3 more in me, then I have to figure out what to do when I grow up

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Maybe the audio is lying to me, but I don't hear any bad engine juju in that video.  I hear a sound like wind blowing through trees (or a whoosh like am radio static) at those points in the video you indicate.

If that's the real sound, it could be your clutch throwout bearing.  That might explain why it lessens when the driveline warms up...

There is something bad in there, I just haven't tuned you guys in yet.   In fact, before it warms up, I am embarrassed to drive by someone in their driveway.  Luckily there are no car guys in my neighborhood

Get to 48 seconds in.  From that 48 second point, you will hear me shift and as I accelerate, I lightly jockey the throttle to start and stop the tapping noise... I shift then I come off and on the throttle, it's when I am lightly "on" that makes the whacking noise sort of like a SBC with a rocker stud pulled out..   .  The exhaust booms a little, try to listen past that, and as you noted there is no bearing noise, exhaust leak noise, or anything other that the "tap/rattle" in the background

Then again at 1:15, when I get into high gear, but as soon as the exhaust booms, it's there but not loud enough in the movie to ID and then you will hear when she leans on the transfer case shifter.

It isn't whatever you are hearing though, and absolutely absolutely no correlation with the clutch other that I need the clutch to take off

RJP pointed me to the plug wires, potentially cross firing 7 and 8.  I will check again, but over the ...2 years...I have chased this noise, I have had the wires all over, but I am going to run them so far apart that it is impossible and see, because if it helps you steer yourself to the noise, the PHYSICAL effect of 8 firing early could explain something similar, but honestly it's just too repetitive and mechanical to me.  It'd almost have to be a crossed wire to be this steady

Last thing, it has to be a huge clue that it gets significantly quieter with engine temp.  Lash of course can change, but I have had every combination of cams, rockers, pushrods, valve covers, in multiple configurations both hyd and solid, and the noise persists.  Every moving "whackable" part has been swapped (fuel pump, eccentric, rockers, etc...even reblocked based on building it loose and thinking the heat could be piston slap)

What remains is a set of pistons that I have visually inspected, measured skirts all in specs and exactly the same as each other, measured pins and pin bores inspected from the bottom, but have never pulled the rings or Zyglo'd and the noise continues in the same behavior it has since the intial build   I hate to pull it down a third time and REALLY hate deduction versus discovery, but I cannot think of anything else that would make a rhythmic beat under light load

I would love to say no noise, but it's there and if I delivered this engine to you, you'd bring it back. 

[My427stang]

Thanks Paulie, honestly I couldn't care less if it was serious. LOL  In fact, I couldn't imagine a part in the engine I wouldn't happily replace and hang the broken one on the wall or happily spiral into the trash.. Now it's my Moby Dick. 

I forgot what your rank is, but it'd be cool to call you Captain Ahab.   

Let's not demote him!  He was up for O-5 last I heard, and that is worth at least two Captains!   On the noise, I had a CJ from the factory that had rod inserts that looked like they were beaten in with a ballpeen hammer.  Warrantied at less than 3000 miles, and the reason for the warranty was a noise off idle and with no load that only I seemed to be able to hear at the time.  The service manager did think he heard something, so they took a look.  Long story short was I got a rebuild and the car was super quick afterwards and no noise.   Joe-JDC

Lieutenant Colonel Ahab just doesn't have the same ring to it, Joe.    Ross will always be Captain Ahab to me, no matter his real rank.   

Colonel Ahab, but, FWIW, that's the same as a Captain in the Navy, so it's not far off

[Joe-JDC]

Congratulations!  O-6 is quite an achievement, and you never know about who is watching for 0-7 behind the scenes.  Anyway, going out on a limb, and saying that if the noise returned on a second engine, then it is not the engine, but an accessory.  Have you checked the damper, pulleys, belts adjustment rods, bolt heads, flywheel, transmission bell housing, starter to headers, headers to bell housing, headers inside where the four tubes are welded into group of four?  I had that one that drove my mad trying to find.  Header flange to crossmember/floor board, engine mount bolts, and lastly transmission tunnel to linkages, throttle linkage bellcrank?  The exhaust grows with heat, and changes dimensionally and that would be something to look at the hangars and attachment points all the way to the back.  You know this, but just trying to come up with a new idea.   Joe-JDC

[My427stang]

Congratulations!  O-6 is quite an achievement, and you never know about who is watching for 0-7 behind the scenes.  Anyway, going out on a limb, and saying that if the noise returned on a second engine, then it is not the engine, but an accessory.  Have you checked the damper, pulleys, belts adjustment rods, bolt heads, flywheel, transmission bell housing, starter to headers, headers to bell housing, headers inside where the four tubes are welded into group of four?  I had that one that drove my mad trying to find.  Header flange to crossmember/floor board, engine mount bolts, and lastly transmission tunnel to linkages, throttle linkage bellcrank?  The exhaust grows with heat, and changes dimensionally and that would be something to look at the hangars and attachment points all the way to the back.  You know this, but just trying to come up with a new idea.   Joe-JDC

Joe I appreciate it, and at some point, you should tell me "Well it has to be something or it is your imagination"  LOL 

The noise didn't appear on a second engine , it appeared when I built the stroker and has continued with every version.   The 390 was quiet, and whatever the noise is, is absolutely in the stroker.  The new 396 is going together as a fun motor I was doing in my spare time, but instead of being for resale, it'll go in the F100 to keep it mobile and prove to me it's inside the 445.

Just to recap

1 - silent beautiful iron head hyd cam 396, very very low compression and not much  power LOL

2
- pulled it out to build a hyd cam 445.  Had this noise immediately
- swapped rockers, cam, pushrods, rockers again, pushrods again, all thinking it was valve train.  At this time went hyd to solid
- standard troubleshooting the entire time


3
- Pulled engine a second time, knew it was built loose, so swapped blocks to get tight bore with the 2618 pistons, inspected everything, replaced a ton of stuff, no smoking gun (though it was at nearly .007 clearance, so I felt good it was piston slap)
- Tried two sets of rockers (Erson and brand new HS on brand new shafts)
- Noise absolutely unchanged
- Replaced a ton of stuff externally

4 - Pulled engine again
- Went through with a fine tooth comb (except for pulling the rings off the pistons)
- Mag'd heads to see if guide was broken, checked all springs, mag'd crank, measured all pins and small ends, replaced flywheel after seeing cracks that were just heat checking, but wanted a steel wheel, replaced clutch after finding odd click in springs in disk and Ram said it wasn't enough for my power, replaced balancer, fuel pump, timing set, eccentric, verified all thrust settings again. 
- Absolutely no change at all in noise.  No worse, no better

Earlier I mentioned that I was in parts replacement mode out of frustration.  I have not only checked everything on your list, I have also replaced everything on your list with new and improved parts whenever I found something even had the potential to be not perfect.  I am not that kind of mechanic and never have been, but at this point I haven't found anything.

The headers have not been replaced, but I checked them repeatedly very closely, and they were quiet on the 390, and the noise started at first fire up of the 445, now years ago. 

I keep going back to a crack in a piston at a pin boss that I missed, or something in a ring land I didn't see because I didn't pull the rings.  It doesn't seem logical to me, but after all the rockers, cams, and even the magg'd heads to check guide movement, I cannot think of anything else that would be rhythmic under light load

[Stangman]

I can hear the noise slightly reminds me of a customer years ago with a stock GTA. He never complained about the noise he knew nothing about cars except where to put the gas in. He sold that car after another 30,000 miles of driving who knows how many with the new owner. But when your saying you make the noise come and go under light throttle is it possible the chain might have a little sloppigg, or hitting something, I know it was said but fuel pump under light acceleration you can't hear those noises just by giving it gas in the driveway. Shit hung over many a fender and engine while my partner drove to find a noise that we just couldn't find, I think it was Plovert that said he would hang over fender and listen if you were nearby I would too. This way you can narrow down the area.

[superduty]

Sounds like a baffle broken loose in the muffler.

[fryedaddy]

i had the wrong header gaskets on mine a while back and it leaked out the bottom of the header gaskets because they were the wrong pattern and they had a tiny gap letting exhaust out.i found it when i looked at the crush on my gaskets.

[wayne]

I can hear it look for a crack in the header tubes they are louder when cold.

[C6AE]

I once dissasembled an engine, I can't remember even what kind it was, just another routine overhaul.
It could have been a Harley. Upon inspection I found a crack in a piston under the oil ring, it went about half way around the piston and was burnished or polished on the mating surfaces of the crack where it had been tapping away for god knows how long.
It was just a fluke that I even noticed it, but I recall thinking "Hmmm, How long has this been like that? I wonder if anyone ever heard it, and how much longer it would have hung on?

(Valve train noises are typically at half cranshaft related noises, I wonder about hooking up a knock sensor to a tach?)

[My427stang]

Thanks everyone, it's absolutely not exhaust, but I can see why it would sound like that.

It seems to be 1/2 speed, but a piston could be that too as the power stroke can be noisy.  The crack in a ring land, or just something I didn't see is where I am leaning.  However, to be honest, I may give it one more college try with a spring swap for laughs.  I have never liked how the damper fit around the guide boss, although it sure didn't look or feel like an issue, and I have a second set of springs from a different manufacturer kicking around, so the couple hours to swap springs is worth the effort.

The knock sensor idea is interesting, if I could log it and identify that noise.  I have had it wired up with blue tooth microphones and that didn't tell me much, too many normal noises with solid lifters for those sensitive microphones

I won't get back to it until next weekend at the earliest, work stuff taking over, but I am still expecting a piston issue