LOUD humming noise *video update - solved

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EJ8 944
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I hate making new threads when there are already 300+ noise issues out there. I need some help though, I am having some problem unlike anything I have read (I've searched and read through close to 50 threads now). But I'm yet to find anyone having an issue quite like this, but it lacked alot of detail so I'm unsure what exactly was going on there. Info below:

Car:
95 S14, stock engine/trans wise, minus a cusco 2-way LSD.

Symptoms:
My car will make a LOUD humming sound on deceleration, and at idle (only if ithe idle is higher then 800 rpm). It's quiet when the engine temp is cold, and gradually gets louder as it reaches operating temp, its the loudest once it's fully warmed up. The clutch being engaged or disengaged has zero effect on the noise. The only way it stops making noise, is if my idle is at or below 800 rpm, or the engine is receiving any sort of load (accelerating or cruising).

The sound doesn't get louder or quieter from speed (from what I can tell), but at higher speeds, I'm assuming because of wind and road noise, it becomes a little less audible to my ears. It's extremely annoying, I can clearly hear it in my car, even over the radio, and outside the car its obviously more audible. Does anyone have any idea what this might be? Or where I can start checking? This is a very frustrating noise to deal with, and it's embarassing to drive around with it making this noise.

I can best describe the sound of the noise as a weak, and almost dead car horn being honked continuously. I've checked all over in my engine bay, the noise definately sounds like its coming from around the firewall by the transmission. It's not effecting the way it drives or anything, it still feels fine driving around. :wtf2:
Last edited by EJ8 944 on Mon May 23, 2011 6:27 pm, edited 3 times in total.


compactfean
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Got me stumped. Lol my best suggestion is get a stethoscope and pinpoint exactly where its coming from. The only thing I can think of is pilot bearing or starter is not pulling back enough (starters sound awful when the bind)

EJ8 944
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I might have to take a video on put it on youtube or something, I don't have a stethoscope on hand, but I'll see if I can pinpoint the location using a screw driver as a stethoscope though.

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Sileighty_85
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sounds like bearings either Diff or Transmission

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OutToWinPAHC
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Could be the TOB or a rear main seal leak in the clutch area. Any oil dripping between the trans and motor?

If not try draining the trans and fill using ONLY GL-4 gear oil, check the FSM for fluid capacity and fill to exact.

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Sileighty_85
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he said the clutch being engaged or disengaged has zero effect on the noise.

So that cancels out the TOB seeing that it would only grind when he disengages the clutch

EJ8 944
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I'll check for a rear main leak tomorrow, and try and get video of this as well.

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240man91
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how many miles on the trans an it could b a berring but most the time when a berring makes noise it gets louder the faster it spins idk? it could bbe a p.b.

EJ8 944
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Unsure, my cluster reads 150K but when I bought the car I was informed that the motor and trans had ~80K. Clutch is relatively new as well (unsure of mileage). What do you mean by a p.b? Pilot bearing?

EJ8 944
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Here is the video for the sound:
[youtube]http://www.youtube.com/watch?v=Q7_WXx3dAHU[/youtube]

I tried to upload the "in car view" video that shows at what RPM range it doesn't make noise(again, 900ish and below rpm = no noise), but my phone was having a fit over it. Anyways, the noise is not over exaggerated in the video, with the hood open the sound is almost scary loud.

EJ8 944
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Forgot to note, the video above, the car is completely warmed up. It is not a cold start.

EJ8 944
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*see above post for video
Last edited by EJ8 944 on Mon May 23, 2011 6:25 pm, edited 1 time in total.

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240man91
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is power steering full

EJ8 944
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I checked my power steering and its a little low, also saw that I have a small amount of MTF on the ground where I'm parking (10-20 drips being parked there for over a month)

I'm not sure if either are related, I thought with low power steering, the pump would only make noise when the wheel is being turned?

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OutToWinPAHC
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Take a wooden dowel and have a friend rev it up and down, poke with one end and listen to the other. you can pinpoint the noise this way withing inches of the area. You can do this for bad injectors, lifters, and all sorts of things too.

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240man91
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yea if the ps is low it can make that noise all the time an when u hit low rpm it will stop but the dowel trick could b helpful to man thas a weird sound.

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240man91
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an how dose it drive? dose this problem hurt the driving of the car?

EJ8 944
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No that's the thing, it drives perfect still. I'll give the dowel trick a try so I can try to pin point the location.

EJ8 944
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Finally got around to fixing this, and I might as well put the final result here incase anyone stumbles on it with the same problem.

Turns out the auxiliary air valve was done, although I'm not 100%, I do suspect that the slide plate was stuck, and this is what was causing the noise.

See the valve here: 1991-1993-240sx-air-regulator-tutorial-t378625.html

1991q45
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Sorry for reviving an old thread but my lil sis altima is doing the same thing. It's a 1995 automatic. The weird thing is this didn't happen till I flushed the coolant system. Where is this valve located?

EJ8 944
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On my S14, it was under the intake manifold, on a vacuum hose that came off the intake I think, real PITA spot to get to.

1991q45
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Is it bolted down to anything? This should apply to the altima too right. I'm hearing the exact same noise.

EJ8 944
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It was a while back, but if I remember right, there are 2 bolts that hold it to the intake manifold.


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