Dear Car Talk...

[ChrisT]

ok so the whole underside of my car is rattling loudly esp. when I turn off the engine or shift at low speeds or idle at low speeds. Perhaps it's just a matter of tightening a few bolts? The vehicle in question is a 95 Jeep Cherokee - manual transmission.

[fern]

is your exhaust system loose?

 

whenever I hear a rattle I have a sophisticated method of localizing the problem. This involves walking around and kicking or whacking various parts of the vehicle until I replicate the rattle.

[ChrisT]

yes that has been suggested to me...however, still too big a wuss to crawl under the car.

[Alan]

Don't you have a decent stereo? I just turn mine up until you can't hear the rattle anymore. Seems to solve the problem everytime.

 

Post 100 for me!

[catbirdseat]

yes that has been suggested to me...however, still too big a wuss to crawl under the car.

Get your better half to do it, preferably with the car in park.

[EWolfe]

yes that has been suggested to me...however, still too big a wuss to crawl under the car.

 

Try turning the car over! Bingo! No more of that nasty under-car crawlage.

 

No charge for the advice.

[Ponzini]

I'll bet it's a loose heat shield somewhere on your exhaust system - you have the classic symptoms. It could also be a loose bash guard around the transfer case or transmission, or a loose gas tank guard plate. Get under there when it's idleing low (or turn down the idle) and feel around.

[jordop]

Another problem for the mechanically inclined: a metalic whining/scraping sound at VERY specific speeds from the front of the truck, only while it (Toyota 4Runner) is in gear. I.e. in neutral there is no sound, only in gear at 40, 60 and 80 km/hr (iie, not brakes). My mechanic gave up, guessed that it was the clutch release bearing

[Trundle]

jordop, it's not a clutch release bearing. That bearing is only activated/operating when your foot is depressing the clutch, not when you are driving in gear. It also would only be related to engine speed (RPM) not vehicle speed.

 

Impossible to tell without hearing it, but I'd lay my bet on a wheel bearing or, believe it or not, uneven tire wear in your front tires.

 

Try one thing before you take it back to a mechanic and rotate your tires front to back. It may make a difference. I've twice been fooled on 2 seperate trucks(both 4wd) of mine by a VERY metallic noise that actually ended up being a tire wear problem that was very difficult to see visually.

 

Good luck.

[Trundle]

I'll bet it's a loose heat shield somewhere on your exhaust system - you have the classic symptoms. It could also be a loose bash guard around the transfer case or transmission, or a loose gas tank guard plate.

 

Agreed. Probably just a loose shield of some type. It could also be made worse by weak or bad motor mounts.

[jordop]

jordop, it's not a clutch release bearing. That bearing is only activated/operating when your foot is depressing the clutch, not when you are driving in gear. It also would only be related to engine speed (RPM) not vehicle speed.

 

Impossible to tell without hearing it, but I'd lay my bet on a wheel bearing or, believe it or not, uneven tire wear in your front tires.

 

Try one thing before you take it back to a mechanic and rotate your tires front to back. It may make a difference. I've twice been fooled on 2 seperate trucks(both 4wd) of mine by a VERY metallic noise that actually ended up being a tire wear problem that was very difficult to see visually.

 

Good luck.

 

I just had the bearings replaced, at the same time the noise started (so maybe he cocked up the installation?), but that tire wear idea is interesting.

[Cobra_Commander]

Get under there when it's idleing low (or turn down the idle) and feel around.

 

Just don't feel around any part of the exhaust system.

[Jake]

Had a rattle in my Jeep that sounds kinda similar to yours and it was the exhaust pipe banging on the frame. Just had to push it around and tighten up some clamps a little.

[Billygoat]

I would say heat shield on the catalytic converter or other loose exhaust parts.

[Ducknut]

Another problem for the mechanically inclined: a metalic whining/scraping sound at VERY specific speeds from the front of the truck, only while it (Toyota 4Runner) is in gear. I.e. in neutral there is no sound, only in gear at 40, 60 and 80 km/hr (iie, not brakes). My mechanic gave up, guessed that it was the clutch release bearing

 

I would agree with Trundle it isn't the release bearing. But could your mechanic have guessed the clutch pilot bearing? It could be the pilot bearing whining at a certain RPMs. That will be a lot cheaper than a transmission synchro which is what jumped to mind.

 

You mentioned specific speeds, but is it always at the same RPM? How about the fan shroud or a busted motor mount?

[jordop]

Another problem for the mechanically inclined: a metalic whining/scraping sound at VERY specific speeds from the front of the truck, only while it (Toyota 4Runner) is in gear. I.e. in neutral there is no sound, only in gear at 40, 60 and 80 km/hr (iie, not brakes). My mechanic gave up, guessed that it was the clutch release bearing

 

I would agree with Trundle it isn't the release bearing. But could your mechanic have guessed the clutch pilot bearing? It could be the pilot bearing whining at a certain RPMs. That will be a lot cheaper than a transmission synchro which is what jumped to mind.

 

You mentioned specific speeds, but is it always at the same RPM? How about the fan shroud or a busted motor mount?

 

More speed specific than RPM specific. I sense it is clutch related since it sometimes makes the same noise when letting it out. Also seems to be aggravated by rough roads for some reason Apparently Toyota clutches are hydraulic and cannot really be adjusted Time for a new clutch anyways

[adventuregal]

My truck has so many rattles I don't think they will all ever go away...

 

On a side note I get a kick out of people who try to imitate the noises of their cars on the radio.

 

[carolyn]

Don't you have a decent stereo? I just turn mine up until you can't hear the rattle anymore. Seems to solve the problem everytime.

 

Post 100 for me!

 

That has saved me so many times!!!!!

[Cobra_Commander]

The midwest represent'n in this thread.

[Dechristo]

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[Trundle]

I just had the bearings replaced, at the same time the noise started (so maybe he cocked up the installation?), but that tire wear idea is interesting.

Very well could have messed up an installation, or it even could just be a defective new part.

 

But could your mechanic have guessed the clutch pilot bearing? It could be the pilot bearing whining at a certain RPMs. That will be a lot cheaper than a transmission synchro which is what jumped to mind.

 

Pilot bearings area also only active when the clutch is depressed. When they go bad they make noise on engagement and disengagement (when you push and release the pedal). Also, it's really rare that a Toyota pilot bearing goes bad. Could happen, but it just doesn't very often. Definitely not a synchro problem.

 

More speed specific than RPM specific. I sense it is clutch related since it sometimes makes the same noise when letting it out.

 

If it is vehicle speed related, you've pretty much eliminated the clutch as the source. Does it make this noise when you are in neutral or first and letting out the clutch? That could be pilot bearing. If it has to be at higher specific speeds, it really seems like a wheel/tire issue of some type.

 

Rotate the tires, if that doesn't work find a new mechanic to diagnose it.

[Ducknut]

 

Pilot bearings area also only active when the clutch is depressed.

 

I beg to differ. The pilot bearing rotates all the time, just provides shaft support when the clutch pedal is depressed. Whatever, sounds like it isn't the drivetrain.

 

Is there such a thing as a car geek thread on cc.com?

[Trundle]

This does deserve it's own geeky forum.

 

Although the pilot bearing is always spinning when the engine is running, it is not alway operating or engaged. When the clutch is engaged, the shaft (connected to the inner bearing) is solidly attached and turning the same speed as the engine (outer part of the bearing). Exactly the same. The inner and the outer bearing are turning together and the bearing is not operating, and definitely not loaded to where it would make noise.

 

No pilot bearing noise when the foot is off the pedal. Except maybe in a rare circumstance when the bearing is totally falling into little pieces... then you would know you've got a problem.

[ChrisT]

well my worst fears were confirmed (and you were all wrong). The rattle under my car is a loose catalytic converter rattling around in the muffler.

[fern]

I was not wrong. Catalytic converter is part of the exhaust system. I suggested it was loose. First reply.