‘98 OHV engine rattle/knock only @ ~2200 RPM

[afast19]

1998 4.0 OHV, 4x4, 5 speed manual, 228k miles
There’s 1,000 posts like this already, and apologies in advance for the length of this, but after scrolling for hours today trying to find someone with my issue I still don’t know what the rattle/knock sound could be. I’m in mechanic school and one of my teachers swears it’s rod bearing knock, but I’d like to know for sure.

I have an engine rattle/knock happening at ~2,200 RPM, and the engine temp doesn’t change it at all. The sound doesn’t happen at idle or above 2,500, but it does happen for a second on start up.
For a bit more info, when I’m accelerating (in any gear) and I get up to ~2.2k rpms the rattle happens as I’m accelerating, but the second I take my foot off the gas or put it into neutral the sound immediately goes away.

VIDEO:
(the video is from when a teacher in my program had me bring it in so she could show some students what rod bearing knock sounds like, I can get a better vid if someone wants)

I didn’t start hearing the rattling noise until after I replaced my whole exhaust. It had aftermarket headers that weren’t fully bolted on and the exhaust was chopped off after the cat (I was getting 7mpg btw) so it was really loud and I don’t know if I just wasn’t able to hear the engine rattle until after I made it quieter or if it coincidentally started happening at that time. I’ve gone only 5k miles since then because I’ve been worried to drive it, but the engine noise hasn’t gotten any worse/better!

The conclusion I’m leaning towards the most is the TSB “carbon knock on acceleration”, but every video for it that I’ve seen on here doesn’t sound similar to my sound, (same with the TSB “sounds like a diesel or marbles in a tin can”).

Work done: (it’s currently @ 228k miles)
*I use Motorcraft 5W-20 oil & Motorcraft filters
@ 216k 04/23 timing chain, spark plugs (Motorcraft), plug wires, & both intake manifold gaskets.
@ 221k 09/23 remanufactured passenger side cylinder head (EngineTech CH1032R), headgasket, both intake manifold gaskets, and passenger side exhaust manifold gasket.
@ 223k 11/23 both exhaust manifolds (Dorman), both exhaust manifold gaskets, y-pipe, gasket between ex. mani and y-pipe, gasket between the y-pipe & cat, tailpipe, all three O2 sensors (Bosch), 3 more spark plugs (Motorcraft), PCV valve, DPFE sensor (Motorcraft), IAC valve, and I removed and cleaned out my EGR pipe as well as installed a new gasket for it. (my cat is hollow but the post-cat sensor is tricked with a spark plug anti-fouler, so I don’t have a check engine light/any codes and my fuel trims are all good)

 

[C420sailor]

hard to hear. Usually a rod knock sounds like a diesel at idle.

2200rpm is the sweet spot for cam chain noise on the SOHC, but this isn’t a SOHC so

 

[410Fortune]

Do you have a mechanics stethoscope?

With that scope to your ear you should be able to determine if it is coming from

The oil pan
The valve cover
Or from the camshaft synchronizer on the back of the engine behind the intake manifold

It is either a valvetrain noise (valve cover)
Or a connecting rod / crank bearing (oil pan)

Or mechanical interference from say a worn cam synchro

Stethoscope and your ears best way of pinpointing the source

 

[Turdle]

That sounds like pre detonation knock.
Check if the crank pulley has slipped causing advanced spark timing. It's possible.

They are 2 piece joined by a vulcanized rubber sleeve wedge thingy.

Might use a piston stop to identify true tdc, then compare to timing indicator to crank sensor reluctor

Triple check firing order on driver side. It's very common to mix that up. Everyone here has done it.

 

[amj441]

Sounds potentially like carbon knock, or a spark knock. Have you checked your camshaft synchronizer? It may be slightly out of time.