3RZ Engine Noise

I hopped on here to see if anyone would be able to help…my 2004 Tacoma has been making this rattling noise when not under load. Revs in neutral will cause it at certain rpm, as well as when i start it. I can also hear it when i slightly let off the throttle above 50mph. I’m pretty confident that it comes from the block, but no mechanics have been able to diagnose. Anyone else having the same issue??
engine was rebuilt and has about 25k miles btw

 

converter heat shields all nice and tight?

Sounds from the block don't normally sound like a rattle as much as a knock.

 

i mean it is more of a knock than a rattle, a slower knock at that. I do have a recording if that’ll help

 

Without a recording we can't help.

 

https://youtube.com/shorts/G48iHebsxc0?si=IgvFuZnyEbcSNg28

here’s the link….i forgot i have to upload it to youtube that’s the only way yall can see a video on here

 

It doesn't sound like it's engine internals from that recording. Maybe a broken cat rattling but it sounds more like something loose/worn on the accessories like the alt or a tensioner. I can't identify it. Did you perhaps drop a socket or a wrench somewhere that vibrates? I chased a rattle on an M3 for a year that was a socket that I dropped into the front cross member. Sheesh.

 

yk i thought it might’ve been a tensioner or something outside the engine. I don’t think it’s something i dropped as it’s only at certain rpm and load

 

just took a close look and noticed something…the pulley closest to the engine block on the harmonic balancer moves back and forth (back to front direction) when throttle is added. Once the throttle reaches a certain point it stops moving and the rattle can be heard. Can the harmonic balancer be the cause of an intermittent noise?

 

Of course. As well as serious running problems when it gets worse

 

update: harmonic balancer replaced. Old one straight up fell apart when i removed it. Runs a heck of a lot better butttt still makes that noise when not driving

 

Does the noise change if the clutch is depressed?

 

its an automatic...sound gets worse when revving while not under load. Someone told me it could either be a lifter or a rod bearing. I figured it wouldn't be a lifter cuz it might be more consistent. I was only thinking rod bearing because as oil pressure builds (when under load) it would lessen the blow against the crank, thus only making the sound whilst not under normal driving conditions. i'm at a loss

 

If it was mine I would remove the belts and run it briefly when it's stone cold and see if the noise goes away. At the least that will eliminate something on the accessories from being the source. But obviously don't run it long without the belts.

 

you ever adjusted the valves

 

i already had the belts off and fixed all the tensioners and made sure was everything was good. It definitely sounds like inside the block. The next step was actually to shim the valves…