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  #1  
Old 11-14-2005, 11:06 PM
Surreal Surreal is offline
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What Causes This Crackling Sound In Cars?

I've noticed that some cars emit a noticable crackling sound from their undercarriage just after they've been shut off. The crackling occurs at a rapid pace immediately after the engine is stopped but gradually fades away after a few minutes. I assume it has something to do with the temperature change, but I'm not certain.

What part of the car is making this noise, and what, physically, is causing this noise to occur? Why do some cars do this while many do not??

Thanks.
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  #2  
Old 11-14-2005, 11:15 PM
n0disguise n0disguise is offline
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It's the catalyctic converter cooling down.
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  #3  
Old 11-14-2005, 11:17 PM
Askance Askance is offline
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That would be the various parts of the car cooling so shrinking at different rates, causing some creaking. The same happens after starting, except it's covered by engine and road noise.

My house, stove, and heater do the same thing.
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  #4  
Old 11-14-2005, 11:28 PM
n0disguise n0disguise is offline
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Just to clarify, the above poster is right, but if you actually get down under the car and zero in on where the noise is coming from, you'll find that it's always (in my experience) the catalyctic converter making the noise.
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  #5  
Old 11-16-2005, 01:58 AM
Car_Guy Car_Guy is offline
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Yes I know this thread is a little old, but I simply have to clarify this.

The crackling sound you hear when shutting off your car is not your catalyc converter. It is your radiator.

Additionally, it is not your radiator cooling down. It is your radiator heating up.

Why you ask? Because one you shut the car off, the water pump and the engine fan are no longer functional. Convection is no longer taking place. The hot coolant sits idley in the radiator tank, thus heating up the surrounding aluminum materials. The filaments in the radiator heat up, expand, and cause creaking noises.

Thats right, folks! Your engine and radiator actually get hotter when you shut the car off. Truth is stranger than fiction.
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  #6  
Old 11-16-2005, 08:46 AM
Xema Xema is offline
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That may be, but I have put my ear close to a catalytic converter and heard just these types of noises as it cools, as n0disguise suggests.

Obviously, such noises can have more than one source.
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  #7  
Old 11-16-2005, 12:03 PM
Mr. Slant Mr.  Slant is offline
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I used to ride my bicycle to school, work and home in heavy traffic, every day.
Cars make a wonderful variety of sounds besides the standard "honk, squeal tires, VROOOM, and idling" choices.
I used to get freaked out all the time when a running car next to me would burp, gurgle, ping, settle (kind of a structural 'ping' sound) and a dozen other weird sounds.
After a while I got used to it. I never noticed those sounds when inside of a car, or as a pedestrian.
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  #8  
Old 11-16-2005, 04:55 PM
BobT BobT is offline
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If you have a hybrid like a Prius, you get to hear the water pump running after the engine turns off. They warn you about this if you read the owner's manual.

That much I figured out, but I was baffled by the dome light.
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  #9  
Old 05-07-2012, 04:49 PM
kellboss kellboss is offline
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Crackling noise from car radiator??

Hi
I have just noticed the past 3 or 4 days a crackling noise coming from what sounds like the radiator, (although I haven't had the bonnet up yet) there doesn't appear to be any water leaking, or stones etc. Does anyone have any idea what this might be, and what to do to stop it?

Please?

Thanks
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  #10  
Old 05-07-2012, 06:00 PM
Mr. Slant Mr.  Slant is offline
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kellboss,

Please start a new thread for your question.
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  #11  
Old 10-24-2012, 09:23 AM
986 fan 986 fan is offline
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Uhhhhhhh you're wrong

Quote:
Originally Posted by Car_Guy View Post
Yes I know this thread is a little old, but I simply have to clarify this.

The crackling sound you hear when shutting off your car is not your catalyc converter. It is your radiator.

Additionally, it is not your radiator cooling down. It is your radiator heating up.

Why you ask? Because one you shut the car off, the water pump and the engine fan are no longer functional. Convection is no longer taking place. The hot coolant sits idley in the radiator tank, thus heating up the surrounding aluminum materials. The filaments in the radiator heat up, expand, and cause creaking noises.

Thats right, folks! Your engine and radiator actually get hotter when you shut the car off. Truth is stranger than fiction.
To the person making this statement, please explain the following to me. I drive a porsche 986, both my radiators are in the front of my vehicle (one on drivers side and one on passenger side) My engine is mid-mounted. All the crackling sound I experience is from the rear of the vehicle, not the front. I would love to hear your "clarafication"
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  #12  
Old 10-24-2012, 09:32 AM
jz78817 jz78817 is offline
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Quote:
Originally Posted by 986 fan View Post
To the person making this statement, please explain the following to me. I drive a porsche 986, both my radiators are in the front of my vehicle (one on drivers side and one on passenger side) My engine is mid-mounted. All the crackling sound I experience is from the rear of the vehicle, not the front. I would love to hear your "clarafication"
Car_Guy hasn't posted here since 2005. You'll be waiting a while.
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  #13  
Old 10-24-2012, 09:33 AM
HoneyBadgerDC HoneyBadgerDC is offline
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The heat shields around the exhaust parts can also put out some noise when cooling off as they are not usually rigidly attached to anything, they tend to get hotter than parts of the engine that are cooled by the cooling system so undergo a bit more expansion.
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  #14  
Old 10-24-2012, 12:42 PM
Omar Little Omar Little is offline
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This is one persistant zombie thread...it's resurrected twice now.
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  #15  
Old 10-24-2012, 01:04 PM
purplehorseshoe purplehorseshoe is offline
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Well, zombies can crackle too, y'know, and they're not immune to the laws of thermodynamics.
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