Odd noise. - JeepForum.com
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post #1 of 19 Old 05-31-2020, 08:42 AM Thread Starter
bruinjeeper
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Odd noise.

Hey guys,

Boy I am starting threads lately like Trudeau is gonna ban YJ's any time now eh?

Anyhow. In the video below, you can hear a distinct sound... hard to explain, but almost like a higher pitched flutey vibration sound. Almost sounds like blowing into an empty beer bottle at the right angle to produce a harmonic.

Could this be a result of my belt on too loose affecting the harmonic balancer? I kept it looser than my usual .5" deflection method when I reinstalled it after the exhaust gasket replacement a few weeks ago. it will be hardly audible through laptop speakers, but it is there in the background... hear it clearly on my phone... and in person it is very noticeable.

i'll give tightening the belt a shot, on that note... what rule of thumb do y'all follow for tightening?





~YJOTM MAY '16, JULY '19~


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post #2 of 19 Old 05-31-2020, 09:56 AM
shaggyjim
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Its just your engine weeping because it wants two more cylinders...[IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_devil.png[/IMG]
To track it down I would first remove the plastic intake and see if that changed it and if not I would remove the belt for a sec and see if that stoped it.
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post #3 of 19 Old 06-01-2020, 05:13 AM Thread Starter
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It'll get 4 extra in 2022.

But these barely broken in (45,000 km) shiny 4 squirrels have some mileage to go before that.

I'll tighten up the belt tonight and see if that does anything, if not, I'll take it off completely as suggested and see if that did anything.

If not, I'll learn to deal.

~YJOTM MAY '16, JULY '19~


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post #4 of 19 Old 06-01-2020, 05:22 AM
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I don't think that's from a loose belt.

Pick yourself up one of these from your favorite parts house, it's amazing how quickly you can find oddball noises with one.... https://www.napaonline.com/en/p/SER835

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post #5 of 19 Old 06-01-2020, 07:06 AM Thread Starter
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I don't think that's from a loose belt.

Pick yourself up one of these from your favorite parts house, it's amazing how quickly you can find oddball noises with one.... http://www.napaonline.com/en/p/SER835
In your expertise, what does it seem like it could be from?

I cant find anything on the net about something quite like this.

I was figuring the loose belt may have something to do with the balancing of the pulley... namely the harmonic balancer. As it does sound harmonic in nature.

On freelance, it seems to be coming in loudest from front and center of the block

~YJOTM MAY '16, JULY '19~


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post #6 of 19 Old 06-01-2020, 07:09 AM
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Does it change with rpms or remain constant?


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post #7 of 19 Old 06-01-2020, 07:51 AM Thread Starter
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Does it change with rpms or remain constant?
I would say no. Just faintly there during idle as you hear in the video.

Thing is... I cannot verify it is there over the engine noise revving.

~YJOTM MAY '16, JULY '19~


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post #8 of 19 Old 06-01-2020, 08:10 AM
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Mix a batch of dishwashing liquid and water, heavy on the dishwashing soap. Squirt around the Harmonic balancer and timing cover. The soap acts like a non oily, non messy temporary lubricant.
You are looking for a repeatable change in the sound to help locate.

You know what the balancer is made of. When they go bad, the rubber shrinks and the pulley part of the balancer moves. Even slight contact with the timing cover can create really funky noises in the beginning before getting worse and sounding like a really bad water pump when it contacts the timing cover harder.

The crankshaft has a certain amount of free-play built in. It can move forward and backward a very little bit. But it's enough for things to make contact some times. At different RPM the crank can move differently. An automatic can also put forward pressure on the crank that changes depending on which gear is selected, the trans internals have a certain amount of free-play too.

So noises can change depending on rpm and their relationship to each other.
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post #9 of 19 Old 06-01-2020, 03:30 PM Thread Starter
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it was a bit warm today, after up to temp for quite a while and the heat soaked in underhood. I popped out of the jeep (no doors)at a traffic light and opened the hood.... no sound at all.

~YJOTM MAY '16, JULY '19~


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post #10 of 19 Old 06-01-2020, 04:11 PM
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If you have an aftermarket cold air intake, I'd bet its reverberating from there. If not.. ?

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post #11 of 19 Old 06-01-2020, 05:14 PM Thread Starter
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If you have an aftermarket cold air intake, I'd bet its reverberating from there. If not.. ?
Interesting note.

~YJOTM MAY '16, JULY '19~


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post #12 of 19 Old 06-02-2020, 02:09 AM
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Quote:
Originally Posted by bruinjeeper View Post
In your expertise, what does it seem like it could be from?
I don't really know, it does sound more air like that metal on metal rubbing though. Although, I've had an idler pulley on a LS motor go bad and make a similar type noise.

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post #13 of 19 Old 06-02-2020, 04:21 AM Thread Starter
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Quote:
Originally Posted by bruinjeeper View Post
In your expertise, what does it seem like it could be from?
I don't really know, it does sound more air like that metal on metal rubbing though. Although, I've had an idler pulley on a LS motor go bad and make a similar type noise.
I would agree.

I dont think it's a rubbing pulley. Definitely hard to pick up on in the video.

But it does sound airy, or a VERY high frequency harmonic caused by a light enough object vibrating very quickly.

Tough to really describe. It is definitely not at my intake though. Confirmed last night. Dead center of engine is where I hear it. The jeep runs smooth and I'm not terribly worried about it
.. more of an annoyance really because it does run so well.

Seeing that the noise was gone yesterday at a traffic light when the bay was really heat soaked threw a wrench so-to-speak in my understanding of it.

~YJOTM MAY '16, JULY '19~


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post #14 of 19 Old 06-02-2020, 05:18 AM
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The dawn dish soap and water in a squirt bottle thingy (not a spray, a stream in this case; mist/spray is for tires) is one of the most useful things in a shop.

I think it’s air

Drive it

A real problem will reveal itself eventually

[size=“3”]Shackles & D-rings are different things.
Cranking IS turning over
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post #15 of 19 Old 06-02-2020, 12:25 PM
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If it comes when cold and goes when hot, it's probably air through metal. Metal expands when hot and will close the gap.

Intake leak would cause high idle or surging idle if its small enough. Could make that sound, but generally it's more of a whistle. Vacuum lines on the intake could also be an issue; however, they generally get worse in heat as they expand and make the gap bigger.

Check the rubber bushing on your brake booster? Use the dawn/water sprayer on it when the engine is cold - same with the upper intake bolts.

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