Mystery metallic engine rattle

July 7, 2025
https://youtube.com/shorts/KO_XD9zOU2Y?feature=share

audio isn’t great but
first 30s or so, very hard to recreate. Sounds like a metallic fluttering, but only happens when lightly revving the engine from idle rpms, and at high vehicle speed. Turning and hills can change how likely it is for the noise to happen.
You can hear it in the low grumble of the engine when I rev. Just sorta sounds…metallic shaking. Sometimes it’s brief, sometimes it lasts 5s or so

I don’t think it’s a heatshield because it is 100% tied to the lightly tapping the pedal
The sound started a few weeks ago, but otherwise it doesn’t sound “bad”, just new and odd.


my ignition coils are probably original, spark plugs are…of unknown age but I’m guessing 80k or only a few replaced here and there. Truck has 284k miles

just wanna make sure I have the right diagnosis before I spend $500 on coils and plugs for no pay off.

No engine codes are thrown.

edit: originally thought this was spark knock. I’ve replaced sparks and coils with Denso and the sound has become clearer, but hasn’t gone away. Also truck runs a bajillion times better.

 

Cheap replacement to start with. It's not like it can't hurt.

 

Does not sound like detonation. Detonation normally happens with near full throttle under load not cruising or light acceleration. If any doubt try filling the tank with a higher octant fuel and see if it goes away.

 

I bought new sparks and coils cus it was something I was wanting to do eventually anyway. I'll try higher octane and some seafoam as well to see what happens.
I'm feeling like power is low, but I could be a bit delusional

 

If you bought anything other than Denso coils - throw them in the trash. Bad coils cause it to buck like a bronco and will give you a CEL and misfire code. Spark plugs only use NGK or Denso. Personally I doubt you need 8 new coils.

 

And don’t buy anything from Amazon for your truck

 

lmao

 

Oh no, I’d never buy from Amazon. I got mine at Walmart from the bargain bin.

 

check/clean MAF sensor. My old 2000 DC - Spark knock under moderate acceleration. Tiny wires had a fur coat of dust built up, throws off the reading to the ECU.

 

That's a good idea, I'll check that thanks. I still have some MAF cleaner from another vehicle.
Thinking on this more, I'm hopeful/suspecting its sparks/coils. Last year when I bought it `shifty helped me find the power steering fluid was being sucked into the manifold and (prior to that, thinking i had a head gasket leak) a Toyota tech commented that my spark plugs looked fouled from coolant.

 

Ok changed all plugs and coils and holy shit my truck became a v8 again.
Clearing EFI and cleaning MAF next, but this was definitely my problem.

Literally feels 2x as light, like I stopped dragging a boat anchor

 

Were the old coils cracked?

 

And what did the plugs look like, for that matter?

One bad coil could've produced that issue, and it should be clear which cylinder was having issues based on the plugs.

 

Well, wish I could say for certain. I didn't see anything cracked, but all the coils looked like sad old plastic.
Spark plugs looked pretty gapped. One was fouled from the power steering fluid that was being sucked I fixed last year. I believe that was back-most passenger side. I recall the needle-point looked rounded over compared to the new one.
I believe the front-most driver side coil looked the worst - meaning discolored and just...sad and weary.

I've only had the truck a year, but it definitely didn't feel this zippy even when I first got it.

Edit: I definitely have leaking valve seals, so the discolored coils might be from oil? Not sure.

 

Not valve seals. Spark plug tube seals. Two very different things. They need to be replaced with the valve cover gaskets, which also often leak.

And the electrode end of the spark plug sits inside the cylinder, so leaking into the plug tube shouldn't be happening if the plug is (at least) hand tight. Discoloring of the coil pack could be caused by a loose plug, firing combustion back up into the tube seal. Or just from heat, it's pretty clear from the discoloration on the heads of the V8/2UZ we've seen that the back half of the engine sees more heat than the front half.

Pointy vs. round - Iridium plugs tend to be super fine-pointy at the end, so if original plugs were rounded out, they were either very fucked from a specific ignition condition, or they were just copper units that were cheap, really old, or both. If the old plugs were regular copper plugs, they're supposed to be changed every 30k miles IIRC, Iridium last twice that long. If you'd never changed the plugs, it's quite possible the previous owner hadn't in waaaaay too long also.

I suspect the spark plugs were the issue, but sure, if original coil packs or aftermarket coil packs were installed, they were probably tired (or inferior if aftermarket).

I think it's important to understand what's inside OEM coil packs to fathom why cracks in the coil pack casings (if OEM) shouldn't cause misfires. It'd take a very deep crack in a very specific place before you reached anything that could arc. Look at the cross-section of an OEM coil pack below and you'll understand why I say that. Notice there's a solid (grey) ground ring surrounding the live/copper parts of the coil everywhere but a 2mm-3mm section at 8 o'clock (blue circle). Below that outer plastic that's cracked (red circle), you'll notice, it's cracked down to the ground ring, and grounds don't arc to ground. Coil packs are thinnest around that outer shield/ground ring, that's really the only part thin enough to crack, not the thicker part in the blue circle. And if you look carefully inside that blue circle, you'll notice the outer part only is a sleeve, so even if that outer sleeve did crack, that next layer of plastic would need to crack in the exact same spot before you started to get into copper, and the chances of that are almost zero.

tl;dr - coil pack cracks are a red herring that get overhyped/blamed for too much shit, without valid reason. However, at 250k+ miles, your truck's factory coils and factory injectors are tired. Anyone on here's truck would likely run like new if folks installed new, authentic OEM injectors and coil packs.

​

 

Thanks for all the info shifty! Wish I paid attention to the coils more lol


I unmarked this thread solved. Just driving a bit today I heard the rattling again. Truck still drives pretty crisp, though hills (big steep hills, I live in mountains) still make me wonder if my truck is missing something else.
Driving uphill unloaded truck shifts to 3rd smoothly, but is only just barely gaining speed as I go up. Curious if this is what others experience? My expectations of a v8 may be just way out there, or maybe this truck is geared in such a way. I thought I’d have torque to spare all the time

Anyway, the metallic “rattling” noise is much clearer sounding now after sparks and coils replaced. I’ll try to get another recording of it.

It happened at low speed, coming out of a parking lot. Once the engine works up it goes away. If I let off gas, it goes away. The volume and frequency is tied to rpm, not speed.
It sorta sounds like something loose rattling, except that it sounds like it comes right from the engine and like I said, the quality of the sound is tied to the pedal.
Wish I had more of a description, I’ll try to get audio of it once more.

I’ll add there’s nothing wrong really going on, other than it sounds like *maybe* something is wrong.

 

Explored around the forum and watched some videos, I think it might be an exhaust manifold leak that goes away as the engine warms up. It certainly is more of a “tick” than any other description I’ve come across.

I saw the videos on flex plate cracked - not that sound at all.

 

If it sounds like marbles rattling, that can be cracked flexplate. A couple of links to videos are in the 'So you just bought a 1st gen tundra' megathread sticky.

Ticking sound ... could be exhaust manifold crack or leak.

 

I’m gonna investigate more this week. But the fact that sound got clearer/more pronounced after fixing my sad combustion makes me think it’s an exhaust leak growing. I’ve never experienced one before so I’m not familiar to say with certainty yet.
just watched Sue replace the manifolds. Thinking I’ll take this into the shop if it is a leak. Studs snapping is too much risk for me xD

 

Here's one way you can test: https://www.tundras.com/threads/hel...ry-high-fuel-trims.160396/page-2#post-3977711

 

Hm I sprayed soapy water on them from cold start and there was a lot of small bubbling, but it’s hard to tell if it’s just agitation from spraying or from a leak. Bubbles evaporated off so quick…just hard to say for certain.
Both sides looked about equal in terms of bubbling. Bubbling did lessen once engine reduced to lower idle though so…
I’m gonna see if it gets worse and am having my mechanic build a quote in the meanwhile.
Maybe I’ll spray again and have my gf flutter the pedal