The truck:
2001 4runner 3.4L, 4x4 limited. Owned it for 3+ years now, purchased with 180,000 miles
198,000 miles. Running 5w30 Castrol high mileage synthetic blend. A few mods, mostly just 881/890 lift with 32 inch Cooper rugged treks

This noise seems to be really well documented by others, and I've dug and dug through many threads to no avail. Here's what happening:

In D or R, with light gas holding rpms at 950-1000 rpm, there's a tapping noise that can be heard under the hood. In P or N, it's not there. It's rhythmic with the engine speed I think, but with the small rpm range it happens, it's hard to say for sure.

Here's what I've done to investigate and what I've replaced. I'm a bit of a maintenance junky, if something was worn and I had it off the truck, I replaced it.

Replaced:
All 3 drive belts. AC idler pulley. Fan bracket bearing. Ignition coils and wires. Retorqued spark plugs. Checked for exhaust leaks. Inspected flex plate with bore scope (didn't see any cracks, but even with the bore scope it's hard to see the hub clearly)
Listened with a stethoscope, found no difference from cylinder to cylinder. Each cylinder has a faint tapping sound which is the mini explosions I'm guessing. Ran injector cleaner with a tank of 91 (half tank, I'm too cheap for a full one)
Checked crank runout and found nearly none. Don't have a dial gauge so I couldn't put a number on it but it's really really minimal
​​​​​​
​​​​​After no improvement, I removed the AC and power steering belt again to try and eliminate the noise. Let it run and there was no noise. So I replaced the AC belt, trying to verify if the noise may be the AC compressor itself, but no luck. Still didn't have the power steering pump belt on at this point. Replaced the power steering pump belt and the noise returned.

I don't think this is conclusive that the power steering pump is the culprit, since it sounds lower down in the engine bay and more centered. Is the harmonic balancer prone to failure, and if so, would it make this noise potentially? If not that, I can't help but believe it's either a valve tapping or wrist pin making noise.

I plan to send oil to Blackstone labs for analysis once I hit 3k on this oil change. I haven't performed a compression test, but I might as well. The trucks always driven great and has good power. Quite frankly, I'll probably just drive it until it gets worse or breaks since it seems so many have this issue and have racked up tons of miles with no change to the noise. I'm at a loss for what to check next, any help is appreciated, I'd love to be able to figure this out, it's killing me not being able to fix it

Videos of my truck:

Driving away
https://youtube.com/shorts/Xy5mzAQ5W5M?feature=share
In gear, revving to ~1000 rpms
https://youtu.be/ZCC5b4CJz7s
Video of another guy who had the same exact noise I'm hearing and is evidently much better at capturing it on video. His sounds more prominent but same characteristics:
https://youtu.be/zE6zf1XVX3o

 

See my responses in this thread


Andreas

 

That's pretty comforting knowing it hasn't been an issue for you over all those miles!