castafly

I have a '98 Tacoma TRD extended cab with the 3.4 motor (approx. 97,000 miles). The engine seems to run fine, and the check engine light has never come on. However, when I accelerate, I can hear some kind of high-pitched vibrating noise coming from the engine. If I accelerate slowly, I can hear it better than if I accelerate fast. I only hear the noise at slower speeds when driving around town or accelerating up to speed on a highway. The pitch of the noise increases as the engine RPMs increase. If I let of the gas, or when the automatic transmission shifts, the noise goes away (momentarily, at least). It kind of sounds like the shroud around the exhaust pipes just behind the engine is making the noise, but I can't be sure, and I have no idea how to correct it. I can't really hear it if I just rev the engine while parked - I only really hear it under load.

On the other hand, I'm wondering if it is engine noise, either valves or a timing issue, or the EGR valve or ?? I haven't replaced the timing belt, and I've never had the valves adjusted (not sure if I need to adjust the valves on the 3.4 motor). Has anyone experienced anything similar? Any ideas about what it might be and how to correct it? The noise is driving me nuts! Thanks in advance!

gpcollen1

I have replaced several bolts on various heat shields on my 99 4runner. I heard the mettalic vibrating / rattling at various rpms and went looking and that is what i found.

good luck

Skrillah

I've experienced the same type of thing you are describing but in a 2.7L, I have yet to diagnose the problem either....

progress4m

I have very similar noise in my 4Runner (1996, 4x4, 3.4L with 98K).
I had it for more then a year. And like in your case: I can't really hear it if I just rev the engine while parked - I only really hear it under load.
After numerous attempts to find it I have only one guess that noise is coming from the inside of Catalytic converter.

ornery

I have a similar problem.. at 3000 rpm theres a metallic ringing noise.. its in any gear, but it doesnt seem to ring with the trucks not moving?

I dont know.. I'm still dealing with the TO bearing ring, and a squeaky drivers seat, and a weird noise from the back slider window.. Stupid truck, haha.

MLiebal

I have similar issue as progress4m
I have a 96 also, but with 196K miles. I am getting a growl under load. Really not so much a rattle, not pinging, but a exhaust leak sort of a noise. Truck still runs very strong, just picked up the noise. I cant seem to find it. I stuffed a rag in the exhaust pipe to check for exchaust leaks and looked for intake leaks. I just dont know?
Any suggestions?

seanz0rz

i have a similar problem with my honda.

figured it was coming from exhaust, so i went through from the down pipe back, playing with it, tapping on it, etc. got to the muffler and heard something strange. spent 2 hours and then finally cut it off. i looked through one end and saw right through the other. all the baffles and rusted out and collapsed and were vibrating on the bottom.

that only solved half my problem, im pretty sure the material in my cat is vibrating around too.

it sounds like tinny metal on metal vibration, like a heatshield. or like dragging cans full of tiny pebbles behind your car.

MLiebal

Thanks Sean!
Maybe that is it. I am going to try running premium gas anyways to see for sure if it is knocking.
Hard to believe it could be the muffler, I only have almost 200K miles on the vehicle (way to go Toyota!). But could be an excuse to upgrade the exhaust.
Will keep y'all posted.
Mike