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nissan
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Discussion Starter #1
Righto ladies and gents, my beloved grenade has developed a rather annoying hooting sound at speed which I can not, for the life of me, figure out.

The sound is difficult to describe but sounds a bit like an owl is stuck on ("Hoooooooooooooooooooooooo"), or perhaps someone blowing over an empty beer bottle (Or a holey piston? :p) and is worst at about 100km/h @ 10% throttle. I always thought it was the snorkel (Sounds like it comes the front-left), but the girlfriend with her head out the window reckons it comes from the back.

It has always made the sound when you back off and coast under light throttle (E.G. down a hill) and will shut up if you accelerate or drop to 0% throttle, but now it seems like it is greatly amplified. It's mainly got me irritated because a) It's really farking annoying on the freeway and b) I hate not knowing what it is. :D

I've checked:
  • Air intake / snorkel - Snorkel was leaking in the guard but re-sealed and no change.
  • Changed air filter - no change, if anything it's louder.
  • Can't see any exhaust leaks, joins are all tight
  • Turbo is still making it's usual whistling and whirring noises and the hooting doesn't seem consistent with when the turbo is working.
  • Intercooler is a yum-cha ebay job (Was meant to be a temp 12 months ago) - doesn't seem to be leaking.
  • Ran out of ideas and checked diff and transmission fluids - all good

I did clobber the exhaust tip when 4WDing, but this didn't start when that happened and there has been no change since I fixed the exhaust tip. No other damage to the exhaust is apparent.

The volume of the noise seems to be largely dependent on vehicle speed, and is barely noticeable under about 90km/h, although if I listen carefully I can still hear it when moving through gears... It changes slightly in tone with engine speed changes.

No other problems, noises or changes in behaviour have been noticed. Apart from the "hoooooo" it still makes its usual noises and still goes like an obese bat out of hell.

The only other thing I've noticed recently is my front crankshaft seal seems to have sprung a leak in the last few weeks... Probably unrelated but worth mentioning in the sake of completeness.

So, if you have managed to read all that... Any ideas? Anyone had a similar thing? Or can anyone at least tell me what causes that "hooooooo" sound so I know where to look?

Don't think I have a signature any more so it's a 2003 GUIII ZD30, 3" Exhaust, Dawes/Needle valve, EGR Block, swirl valve disabled with 267,000km on it.

Cheers,

Thomas
 

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LED ZEPPELIN
1995 GQ TD42 NA
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12,022 Posts
Warped exhaust manifold, or cracked EGR pipe (goes from the rear of the exhaust manifold, around the back of the head close to the firewall, then forward to the EGR valve assembly).
 

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nissan
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Discussion Starter #3
Hmm from the threads I read I was under the impression that would cause a much higher pitched sound (More like a boiling kettle)... EGR Pipe I can check, I imagine I need to at least remove the heat shield to check for signs of a leaky exhaust manifold though?
 

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Y2KGUII ZD Wgn
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Hmmm! very thorough fact file. I think you really need to concentrate on honing in on an area, there are so many things it could be, manifold leaks usually sqeek/squeel, exhaust leaks can make all different sounds as can failing mufflers. Sounds like this are very hard to trace unless someone can define an area, is the girlfriend sure it is coming from the back? Do you have a roof rack and had anything change recently? Could also be an ill fitting weather shield.
 

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LED ZEPPELIN
1995 GQ TD42 NA
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Exhaust leaks sound like a slipping fan belt.

Yep you can't get near the EGR pipe that goes behind the engine without pulling the heat shield.

Usually exhaust/EGR leaks go away once the motor gets hot and everything expands.
 

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nissan
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Discussion Starter #6
Yeah, it's more of a lower-pitched, 'fuller' sound than I would expect from an exhaust leak. I might pull the dash cam footage and see if it is apparent on the video.

I may need to start thinking outside the box... I've been focussing on either intake or exhaust as responds to throttle input, but at the same time, is loudest at highway speed.
 

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LED ZEPPELIN
1995 GQ TD42 NA
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My CRD GU was making a god-awful screeching sound when cold, it went away after a few minutes of driving. It sounded like a slipping belt on whatever the devil drives. I did the research, and took it to Nissan to have the "known" belt tensioner problem rectified (at 70k on the odo).

They said the tensioner was fine and that it was the alternator, they replaced it... no noise when I took the vehicle back (warranty fix).

Next day - squeeeeaaaaal. It was a cracked EGR pipe.
 

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just a good guy.
2009 gu ute
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mine was doing the screaming belt noise turned out to be warped exhaust manifold . does it make noise while stationary and revving,
 

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nissan
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Discussion Starter #9
Okay, it's not great, but you can sortof make it out in this video (Although I'm sure it's easier for me to hear because I know what it sounds like):

https://www.youtube.com/watch?v=QC8Xd_m67g8

It actually sounds a bit more like a whining in this video... Maybe I haven't had enough coffee today but I'm struggling to find the right word to describe the sound.

EDIT: Just to clarify from the first post, I thought it might be turbo related at first (Maybe it still is), but the pitch of the noise is the same if it's at 14psi or, say, 5psi.... Although at 10% throttle semi-coasting when it's loudest I'm usually about 5/6psi.
 

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LED ZEPPELIN
1995 GQ TD42 NA
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The noise in the video sounds like wind noise - a rack, or similar.
 

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nissan
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Discussion Starter #11
I do have a rack with various bits hanging off it, though I've had that for a while... I did check though and can't see anything obvious that has changed.

Just went for a quick drive with the missus putting her ears in various places around the interior - She has changed her mind and is now sure it's coming from the snorkel - At least that's where it is loudest. Took the ram head off and makes no difference.

It's definitely loudest at above 90km/h, very little load at 10% throttle (Thou shall count to 10%, not 9%, not 11%) - Going up a hill above 90km/h 10% throttle it won't do it.

At least for now I will focus on finding any changes in the intake... I'm not too familiar with turbo's, could it be turbo-related? I would have expected horrible screeching or shagged-bearing type noises coupled with a loss of performance if there was something wrong it, but then again, I have never experienced a turbo problem

Anyway, thanks for your input so far and apologies for being a bit verbose :D
 

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Nissan
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Hows your tyre pressures?, wouldn't make much sense but you never know
 

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nissan
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Discussion Starter #13
Tyre pressures are good, also made me think to checked hubs and they aren't locked.

This darn noise is a houdini owl, seems to move around.

I realised I'd forgotten about one category of changes I'd made though. I replaced the upper + lower control arms, rear uni joints and flipped the tailshaft. Used the adjustable uppers to correct the pinion angle (Despite having the lift for 4 years replaced the arms now due to bushes causing a clunk). This was probably a week or two before I noticed the howl.

I doubt it's a whine from the drivetrain somewhere but having a relation to vehicle speed could mean it's worth checking out.
 

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Y2KGUII ZD Wgn
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Tyre pressures are good, also made me think to checked hubs and they aren't locked.

This darn noise is a houdini owl, seems to move around.

I realised I'd forgotten about one category of changes I'd made though. I replaced the upper + lower control arms, rear uni joints and flipped the tailshaft. Used the adjustable uppers to correct the pinion angle (Despite having the lift for 4 years replaced the arms now due to bushes causing a clunk). This was probably a week or two before I noticed the howl.

I doubt it's a whine from the drivetrain somewhere but having a relation to vehicle speed could mean it's worth checking out.
I doubt very much that the aerodynamics of the chassis and components would create howls, there is just too much crap under there with major deflection happening from front to back.

If it's emanating from underneath it is most likely due to exhaust anomalies. I get one at around 1800rpm in 5th and that is from my roof rack but it passes quickly. Why not get a bit of stiff cardboard and make a temporary air dam for the front of the rack and see what happens, like wise turn your snorkel head around and try it (not suggesting you leave it there just try it).
 

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Discussion Starter #15 (Edited)
Righto, I took the intake pipework apart the other night to inspect for any splits or leaks... Couldn't find anything obvious, the intake did seem to have a fair bit of dirt stuck to the sides (Didn't get any pics) but I am hoping that is just 12 years / 270,000km worth of build up. Could find any evidence that would suggest it is recent dust ingress anyway.

While I had the pipes off I took the little elbow off the turbo inlet (Only because it was right there) and had a poke at the compressor wheel... Slight side-to-side play but didn't notice any in/out play. To my untrained eye the blades look fine.

Not sure what that yellow mark on one of the blades is though. Probably should have checked it out while I was there:




Went for a drive today with ECUTalk on the computer to data log but couldn't note any anomalies. Also had the gopro in various places around the car but it didn't really clarify anything. Could post the video but the gist of it is:

90 - 95km/h @ 10% throttle, minimum load (E.G. downhill). ~5-6PSI - Sound is loudest
90 - 95km/h @ 10% throttle, moderate load (E.G. uphill). - Sound goes away
90 - 95km/h @ 40% throttle, any kind of load, ~ 12PSI - Sound dies down
90 - 95km/h @ 0% throttle - sound completey gone

100 - 105km/h - Sound as above but pitch is higher, volume quieter.

80km/h - sound as above but pitch is lower, volume quieter.

seems to be louder at the front (Difficult to hear when the gopro was on the back window)

The design of the snorkel means I can't really turn it around, but I did take the head completely off and it made no change. Still yet to try the cardboard on the roofrack though.

I'm actually starting to question my own sanity a bit and perhaps it has always been this loud... As I mentioned it has *always* been there but I've never noticed it this loud. Maybe I should just turn the music up and pretend it isn't there :D
 

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NISSAN Patrol DX 6.5Ti Chev Optimizer
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I changed my water pump last week and the new one came with a new viscous fan hub, mine is now making a similarly hard to describe noise but I can confirm that it is the new hub working where the old one wasn't.

Maybe check that your radiator fins are clear or mud etc.
 

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Y2KGUII ZD Wgn
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Turbo is perfect :), wish mine looked like that, still works fine.... Just another thing to check, are all the screens in the airbox lid? that makes a considerable difference to sound, they don't just fall out but have a look anyway, should be 3 of them.

my turbo1.jpg
 

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Discussion Starter #18
Ouch! How did that happen?

Yep, still got three screens, one on the lid just above the filter then one on each side where it joins to the MAF housing.
 

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Y2KGUII ZD Wgn
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I went a bit too big on the pre turbo nozzle a while back, Hasn't affected performance so I must be just on the cusp. Have gone Pre turbo again but with a different perspective this time :).
 

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Discussion Starter #20 (Edited)
Who likes mysteries?

Tonight, trying to eliminate recent changes, I swapped the tailshaft back the normal way around, and reset the pinion angle close to what it previously was (Adjusted the upper arms out to roughly the same length as factory). At this point the pinion angle is actually incorrect (Not parallel), though, it has been like this for the last 4 or 5 years I've had this suspension.

Went for a spin and, at this point, the owl seems to have quietened back down to normal hooting levels. Keyword here is seems, I've had enough for tonight but need to drive into work tomorrow so that will give me a run on the freeway to test - it's entirely possible it's just a placebo, so will compare dash cam footage of the freeway sections.

EDIT: Also, dear moderating overlords, if you feel this is better suited in the GU section rather than DI specific, feel free to move :)
 
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