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Discussion Starter #1
So a couple of weeks ago, my truck started making this short "pew" noise directly after it starts when the engine is cold. Only last like a second and it happens just as soon as I release the key from starting. Seems to be worse if its colder outside but will even do it when its above 60F. Once the truck has been driven and reached operating temp, it will not make the noise when you start it again. the truck pretty much needs to sit for a day and completely cool to make the noise. The truck starts just fine, runs and idles just fine. I have an Insight CTS and all temps and pressures are the same as they always have been. The truck is up to date with all maintenance. I have realized though that the noise started directly after an oil change! I changed my oil on the 5th and I first heard the noise on the 9th and its very possible that I didn't drive any between those days. Changed oil with 10qts of Rotella 5w40 and a Mobil 1 filter, same as always. The only thing I did different was I changed out my factory oil drain plug with a PPE magnetic plug. Feel like this shouldn't be related but its the only thing "different" I did during the oil change. Please see link for video of noise.

 

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Discussion Starter #2
OH! Forgot to mention that I recently (after the noise started) changed my belt, both idlers, and the tensioner. So the noise should not be belt related unless the alternator or power steering pump is causing it.
 

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Discussion Starter #3
Anyone have any ideas?
 

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My 12 will cycle turbo vanes right after started. MAYBE this is what you are hearing.
 

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I've seen lift pumps wired into a "HOT" that goes cold when the key is in the "START" position... so you turn the key on to RUN and the pump starts and builds pressure. Then when you hit "START" the engine cranks, but the pump shuts off and the pressure falls. When you release the key back to RUN, the pump restarts. Maybe this is the "pew" sound you hear.

Its pretty easy to trouble shoot it, just pull the fuse out and see if the noise stops.
 

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Discussion Starter #9
lift pump?
I have considered this as well. The lift pump has been installed for about 3-4 months and I don't ever recall hearing this. But it is worth looking into. I am considering picking up a cheap mechanics stethoscope to see if that will help track it down. Truck runs too well for it to be anything serious. Would just like to know what the heck it is.
 

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Discussion Starter #10
My 12 will cycle turbo vanes right after started. MAYBE this is what you are hearing.
Nah, my veins cycle all the time. Im use to that noise, this is different
 

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Discussion Starter #11
I've seen lift pumps wired into a "HOT" that goes cold when the key is in the "START" position... so you turn the key on to RUN and the pump starts and builds pressure. Then when you hit "START" the engine cranks, but the pump shuts off and the pressure falls. When you release the key back to RUN, the pump restarts. Maybe this is the "pew" sound you hear.

Its pretty easy to trouble shoot it, just pull the fuse out and see if the noise stops.
Perhaps you are right. Might have to look into this further. Just didn't do it before and the pump has been installed for 3-4 months. Pump pressure hasn't changed. I could also use my test light to see if it looses power during the crank. Good suggestion, thanks!
 
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Discussion Starter #12
lift pump?
I've seen lift pumps wired into a "HOT" that goes cold when the key is in the "START" position... so you turn the key on to RUN and the pump starts and builds pressure. Then when you hit "START" the engine cranks, but the pump shuts off and the pressure falls. When you release the key back to RUN, the pump restarts. Maybe this is the "pew" sound you hear.

Its pretty easy to trouble shoot it, just pull the fuse out and see if the noise stops.
Only thing, if it is the lift pump, wouldn't it do it after every startup? Not just when the engine is cold? Maybe,if it is the lift pump, there is an explanation for it only happening when the engine is cold :confused:
 

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Discussion Starter #13
Okay guys, I am stumped and am pretty much giving up. So I bought a mechanics stethoscope to assist in finding this noise and a buddy and I listened around the truck as my wife started it a few times. No noise coming from the belt area or any pulleys. I used the stethoscope to listen to the starter, passenger up pipe/egr, oil pan, and lift pump with no luck. Then we noticed that the noise seemed louder from the passenger side wheel well. So then we listened to the oil filter (Mobil 1 which only has a few hundred miles on it as I just changed my oil). It sounded like the noise was coming from it, which would also make sense as the noise started right after my oil change! There was also a constant squeal from the oil filter that could only be heard through the stethoscope at idle. I assumed that I must have got a defective filter, maybe had something wrong with the bypass valve. So I switch it out to an AC Delco filter and called it done. Well when I started the truck this morning, I heard the same, familiar "Pew." As of now, I plan to listen to the water pump next cold start, drivers side up pipe, and the new oil filter. If I am still unable to locate it, to hell with it then. The truck drives too good for it to be a "problem," boost pressure is good, oil pressure is good, coolant and trans temp are good, fuel pressure is good, turbo veins cycle just find and sound normal, balance rates are good. Literally everything that I monitor on my truck is how it always has been. I will just drive it and if something is "broke" or going out, it will tell on itself eventually.
 

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Discussion Starter #14
Just an update on this, in case anyone else has this happen. The noise was my power steering pump. The fluid was old and beyond burnt. I ran 6 qts on new fluid through the pump and the old fluid was so black that it still has some color to it even after running the 6 qrts. It is currently lighter than ice tea so it loads better than it was. But this noise went away after only running 3 qts of fluid through the pump. So the old fluid was definitely the culprit.
 
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Oh man! thanks! I spent far too long trying to describe the sound in google searches before stumbling on this. "Pew" sound is good description and my truck's cold startup sound is exactly what your video is.

Going to change the steering pump fluid! Thx for updating your post - always helpful when people do that instead of just posting questions never updating with the solution.
 
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Discussion Starter #16
Oh man! thanks! I spent far too long trying to describe the sound in google searches before stumbling on this. "Pew" sound is good description and my truck's cold startup sound is exactly what your video is.

Going to change the steering pump fluid! Thx for updating your post - always helpful when people do that instead of just posting questions never updating with the solution.
Hope this is whats going on with you too, easy fix. Make sure to get plenty of fluid, it took a lot to get mine "clean." It was the blackest fluid I've ever seen! I haven't been in any very cold weather since I changed mine, but it would make the noise at a cold start if it was any temp below 70F outside. Coldest I have been in this Fall is in the 50s, no noise so far!
 

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Hope this is whats going on with you too, easy fix. Make sure to get plenty of fluid, it took a lot to get mine "clean." It was the blackest fluid I've ever seen! I haven't been in any very cold weather since I changed mine, but it would make the noise at a cold start if it was any temp below 70F outside. Coldest I have been in this Fall is in the 50s, no noise so far!
Ya mine just started doing it at 25F. Hate to admit it but ive got 330,000 kms on the truck and have never touched the PSF. Bought the truck at 170,000 kms so who knows if the original owner did anything. Going to be some serious toxic waste coming out of there.
 

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Discussion Starter #18
46F out this morning and no noise at all when I started the truck this morning. Before, it could be a sunny afternoon, 68F out and it would make the noise.
 
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