Need the group's help- new sound my 4Runner is making that can't be healthy. Is this what a knock sounds like? Doesn't sound like a rattle to me.

2008 V8 SR5 with 58K mi. Never had any issues with the truck, oil changes every 5K miles but never had any other fluids changed or any other periodic/preventative maintenance done.

Some notes:
- I noticed this sound for the first time maybe 6 months ago
- It is clearly coming from the engine compartment, maybe just forward of the steering wheel but hard to tell
- It's intermittent and only happens (or I only notice it) about every 10th time I drive
- Happens most frequently within the first few miles but have heard it well after it was warm
- Most clear when at idle but can make it out at speed also
- AC/defrost/fan not on when I hear it
- It is getting louder with time but not any more frequent

I recorded the sound with my iPhone from the driver foot well. When I play it back on my phone I can hear it clearly but it's still very faint. For some reason when I turn it into a file that can go on YouTube, it gets even more faint. When I play it from YouTube on my phone, I can hear it clearly but it's gotta be right at my ear.

WTF is this noise?

Posted on YouTube here

I can hear a cyclical bumping. I call it bumping because tapping would (IMO) be a metal on metal higher pitch sound. This has a metal on plastic sound. It appears to be lasting 1.5 seconds per cycle.

I wonder if there is a lose bolt(s) on your air intake or similar plastic piece, and the natural engine vibration is causing the plastic piece to reverberate against the engine bay.

Have you been able to replicate this with the hood up?

Yeah, cyclical is a great way to describe it.

I haven't been able to listen with the hood up because I always hear it on the road and haven't ever just pulled over and lifted the hood. Have opened the hood with it running multiple times but never been able to get it to do it when I want it to.

I've given several things under the hood a good shake trying to determine if it is a rattle of some sort but nothing has been loose or made that sound. Also, if it were something just loose I feel like it would do it with more consistency.

There are rattles in my vehicle both forward and rear that will rattle for a day or a few hours, then go away for a couple weeks. It's weird as ****... Seriously.

I would guess if you don't hear it while you are in park, then you must be in drive (brakes depressed likely) and torque placed on the vehicle is what is causing your noise.


I am going out on a very small limb here, with no knowledge of your situation and I'm sticking to my guns. The engine is imparting a harmonic vibration on a bit of plastic in the engine bay. replicate it by having somebody sit in drive, brakes on, and your head in the engine bay with the hood up.

I'll try that this weekend.

Anyone else have an idea? I take her in for an oil change in a couple of weeks and am going to ask the dealer to try and figure it out. Would be great to be able to give them some starting places, assuming I don't find it myself this weekend.

I honestly can't hear anything in that video...

So its a loud knocking sound?

Yeah, I can't pick it up on my computer either, only if I listen to it on my phone.

Anyway, it's a barely perceptible sound that, like Minn3sota stated, sounds like something on a cycle. His timing is spot on too- it's on like a 1.5 second cycle.

I'll see if I can find a way to get the sound posted so you can actually hear it.


Edit: just posted it a different way to Youtube here. Sounds better to me. Hopefully the rest of you can hear it and tell me what in the hell it is.

Well, without being able to hear it...

-Does it change with engine speed/RPM?

-Does it matter if the vehicle is in Gear/In Motion or stationary?

-Have you tried looking under the hood for the sound?

Try this link, maybe better: https://m.youtube.com/watch?v=9bRsae...m-upload_owner

Is it the noise that sounds almost like a cat purring or someone breathing hard?

If you have a go pro or some other camera stick it in the engine compartment and drive it. You should be able to pick up the noise and maybe even see the issue.

Ive duct taped cameras under my rig many times to determine where a noise is coming from or assess whats moving around...

I hear it clearly from your video. Never heard it before. It is very rhythmic or better said, musically its keeping a perfect beat when its going...

Almost like something is winding up and then releasing creating the noise, winds up again and then is released/breaks free in the fluttering/knocking noise.

Your not alone,I have the exact same noise. 07 limited v8 here, and i primarily hear it on cold startups, it typically doesn't last long after I start driving the vehicle. Mine seems to be louder when the truck is in gear and foot is on the break. I was thinking it could possible have something to do with emissions...

Yeah, cat purring. Good description.

No GoPro, but have pals that do. I'll try that.

Yep, good description.

Have you ever heard it while you're driving? Mine sounds exactly the same at speed as stopped- same cyclical pattern (not faster or slower), same volume, same everything, just harder to hear against the road & engine noise when driving. Weirdest damn thing.

My guess would be the brake booster. That is located in the area you say the noise is coming from and wouldn't be impacted by engine speed.