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What is this engine noise: scraping/chirping

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What is this engine noise: scraping/chirping

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Old 09-08-2018, 11:45 PM
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Question What is this engine noise: scraping/chirping

First off, this is my first post here so forgive me if I've committed any high crimes; feel free to correct me or give me pointers on posting.

I have a 2008 S p!g with 107k miles on the odometer that is making an intermittent scraping type sound from near the top/front (?) of the engine that comes and goes entirely, even when the engine is warm. It generally starts anywhere from 30 seconds to 3 minutes from when I start the vehicle. It usually lasts for a few minutes, recurring every 3 to 8 minutes or so. I'm having a hard time figuring out precisely where it's coming from. Here are some facts about recent changes to the vehicle that may or may not have anything to do with the issue:
  • I've noticed more blue smoke coming from the exhaust recently during cold starting (a pronounced puff that then disappears rapidly) though this may be a coincidence but thought it worth adding in case it could be related. It does coincide with when I noticed the noise but again, this may just be because I starting paying more attention to it recently.
  • We very recently relocated from Texas (where I always ran 93 octane) to northern California where I have to feed it 91 octane fuel for now.
  • Upon hearing this noise, I assumed it was the water pump (due for replacement anyhow) or pulley, so I replaced the pump, thermostat & housing, pump pulley, tensioner roller, left and right idler pulleys, the belt and did a coolant flush. This made no difference; the noise is still there, just as before. I did not replace the tensioner strut as it seems to be strong still and belt tension seems good but I'm no expert.
  • I changed the plugs and coils (to latest/updated OEM version) about 100 miles before I noticed this noise. Guessing that's not related but seems worth pointing out as well.
Here's the video with the noise:
.

It disappeared again for about 5 minutes right after I stopped filming.
Any educated guesses? Valve guides? Lifters? Bearing in alternator or steering pump? Angry crickets?
 

Last edited by suspectdevice; 09-09-2018 at 01:03 AM.
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Old 09-10-2018, 01:31 PM
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Do you have a mechanics stethoscope? Harbor Freight has one for $3.99. That should help you narrow down where the noise is coming from. It certainly could be an alternator, AC compressor or power-steering pump bearing - except I can't recall ever hearing about one failing on a Cayenne.

I did notice - you're missing the two plastic locking pins that hold the Y snorkel onto the throttle-body. Those are sort of important, and you may want to address that. Dunno if them being missing might be the source of the noise - but they ARE supposed to be there, so..
 
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Old 09-10-2018, 04:23 PM
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Thanks for the tip - I hadn't heard of a mechanics stethoscope until now but I'll grab one and give that a try. I'm guessing it may be difficult to get the wand down (or up from below) close enough the alternator given the tight space and spinning belt right by it but I could be wrong. I've spotted one on Amazon that also includes a directional sound "horn" along with the usual wand so if the wand can't reach safely, I'll try the horn thing.

Also, as for the pins, those were only out temporarily (was finishing up some final reassembly when I captured the video) but it happens whether or not they are installed. Good eye though for catching that!

Thanks, again. I'll report back my findings.
 
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Old 09-14-2018, 02:00 PM
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After a bit of probing with the stethoscope, it appears to be coming from near the throttle body. When I place the probe at the top back edge of the throttle body, I can hear it the clearest, though it still sounds slightly removed from that location, almost like it's somewhere well behind or below the butterfly. Also, the chirping sound is in sync with the sound of the purge valve and line "pulse" so I'm looking for a vacuum leak there but not finding anything obvious and the chirping does not seem to originate from the purge valves or line itself.
Anyhow, still poking around, but that's what I've got so far. Maybe that rings a bell for someone and might give some better clues?

A few other facts:
- there's no CEL codes thrown (yet)
- when I rev the engine (in park) the sound is identical for just a moment in frequency and pitch and then disappears but when it returns to idle it typical returns immediately in its original frequency and pitch.
 

Last edited by suspectdevice; 09-14-2018 at 02:10 PM.
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