Mystery metallic engine rattle

I'd need to hear the sound, honestly, to know if it's a manifold crack, knocking, etc.

There's a few things that would cause knock, ignition/detonation issues is one of a few, so is using too thin of oils, you'll get bearing knock, and lack of oil uptake (either from too little oil, pickup tube being clogged) is another.

On the latter, that's why, if it started after an oil change, I'm instantly skeptical if they used 0w20 instead of 5w30. Would it realistically result in knock? I'm not sure it would. You don't have VVTi, so there's less reliance in your version of the 2UZ than the one we have in the 2005-2006.

If you truly believe it's on a single bank, because it audibly sounds that way, I'm skeptical if it's oil related (but again acknowledge it'd be weird if it started right after an oil change). Given single bank activity, if I wanted to know if it's related to ignition on a specific cylinder (bad plug, bad coil, bad injector), I'd unhook, one at a time but never two at once, and only for 3-4 seconds to listen for the sound to disappear, the coil packs on 1, 3, 5, and 7 cylinders. Unhook one for 3-4sec, does the sound go away? If no, move to the next.

If you find unhooking one specific cylinder makes the sound subside, I'd be turning my attention to the plugs and coil pack. Knowing the driver side cylinders are numbered front to back as 1, 3, 5, 7, say unplugging cylinder 3 eradicates the sound. Turn off the engine, and swap the coil packs between cylinders 1 and 3. Assuming the sound is still there, repeat the unplug test on cylinder 3, and if the engine sound doesn't change (i.e. issue seems resolved), test on cylinder 1. Does the sound go away? If yes, you know that coil pack is furked. If the sound remained on cylinder 3, then you know it's either the plug or maybe the injector on cylinder 3. Easy enough: Pull that plug and inspect it, and if it looks OK, swap that plug from cylinder 3 with the plug in cylinder 5. Does the problem move to cylinder 5? If yes, it's time to install new iridium spark plugs.

Just don't overtighten your spark plugs or use anti-sieze or similar on them. Like oil filters, you don't need to overtighten plugs. Get them nice and snug, hand tight plus a quarter turn in most cases has been my experience.

Others may be able to chime in with their thoughts too. But a video or audio clip would help, greatly. Because, like, if it's a thumping sound, it may just be you have a vacuum hose loose and you're hearing the sound of vacuum pumping.

 

Thx for the insight. I'll focus on getting an audio clip next. It's holding us back.
Sound only happens while moving so...don't think I can't unplug a plug and check if the sound stops xD

ChatGPT says to scan for codes even though there's no CEL, so I'll do that too

 

Sorry, I thought you would've checked for codes already, or noticed the check engine light on. I guess also make sure the check engine light is working, since 2000-2004 trucks can have the bulb burn out. That light should turn on when the key is turned forward while the vehicle is off/not started. If you don't see it, the bulb may be toast.

That said ...

Wait ... I must've missed something, I thought I read the sound happens when you tap the gas, making RPMs climb. Do you not hear the sound with the hood and driver door open, in PARK, and you step on the gas to rev the engine? What about in NEUTRAL?

It only happening when the vehicle is in gear, and when accelerating, those two are, I think, pretty important symptoms. Especially if it doesn't do the same while in P/N gears.

 

I only hear the sound while tapping the gas *while moving*
It *usually* happens when the engine load lightens. So imagine cresting a hill - right as I get to the top and the hard part is over, transmission up-shifts, I'll usually hear this rattling/clattering sound from the engine as I lighten my foot on the gas or flutter it. Not like a BANGING sound, just a 'knocking' sort of noise.

I can get the same effect driving gently through town *after* being parked for a bit (warm start).

*Rarely* I will hear it under heavy load (like when climbing a hill), and if I do hear it under heavy load, it's not as loud.

If I'm parked or just stopped at a red light - no sound no matter how much I flutter the engine.

The sound is DEFINITELY NOT coming from under me around the transmission. Shifts are smooth as hell. Nothing about the drive feels or seems wrong other than this noise.

NO CEL LIGHT, which is why I didn't check yet. I have a reader, will do that today.


On a cold start, I usually won't hear the noise until 20-30mins of driving

 

Also, maybe this is relevant or maybe not, but recently I drove 3 mins and saw my coolant temp went to red + heard groaning from the engine bay.
I guessed it was a stuck thermostat, decided to whip around back home. Hit a pothole and temps suddenly dropped back to normal and groaning stopped.

I have a replacement thermostat ready to go, I'm assuming that groaning was the water pump fighting a stuck thermostat and I just bumped it loose.

Doesn't seem relevant to this engine noise to me, but hey ya'll are smarter than me

 

I would get back to this after replacing the t-stat. I suspect the sound and t-stat issue may be related. Remember, jiggle valve needs to be oriented at high noon (11-12-1 o'clock) at install.