Jackhammer sounds from under front end and other horrible noises - 2008 Yukon Denali

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Gildan

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OK, let me give you the progression of this jackhammer sound coming from under my the front end of my 2008 Yukon Denali (170K miles, well taken cared of, checked out and completely serviced not one month ago):

About a week ago, I was driving along and heard what sounded like a cross between a plastic trash can stuck under the vehicle and someone spraying high pressure water under the passenger side wheel wells. It was loud. Ear splitting loud, about 120 db without any exaggeration. The first time it happened it lasted about 5 seconds and appeared to come from under the whole passenger side. Then about 30 seconds later it sounded like it was coming from directly under the engine (just like the splash shield came down and was scraping along the road). Ear splitting loud. I pull over and see nothing under the car at all to account for the sounds.

Fast forward to tonight. I was backing up at my horse barn and heard a nasty banging noise, like someone beating on the front end with a hammer when I backed up and turned the wheel to the left. I tried to reproduce this sound by repeating the maneuver and got no banging sound. So, I straighten out and drove down the driveway and the banging sound came back, but the rate of it (about three times per second) did not change with the speed of the vehicle. The banging stopped and was replaced by a hissing-squealing sound. This hissing-squealing sound stopped the second I stopped the vehicle.

About two minutes later, there came a sound that was ear splitting loud that resembled a jack hammer that started at about 25 mph as I slowed down for a deer in the road. The jack hammer sound only stopped when I came to a complete stop. I drove on and the hissing- squealing sound continued for about 5 miles and stopped when I went down a big hill. That sound was replaced by what sounded like loose metal bars clanging together every time I hit a bump in the road, almost like a loose suspension part. That stopped about about a mile.

When I got home, I lifted the front end and inspected for any looseness in the wheels, spun the wheels to listen for bearing and CV joint sounds, etc., and did this also at the extremes of the steering. Nothing, No looseness in the half shafts/cv joints. Nothing. I then took the Yukon out of a test drive - nothing. It performed perfectly, no unusual sounds or steering issues at all. I tried to reproduce the exact conditions by going back to the barn and retracing my exact steps at the exact same speeds, etc. Nothing. Everything seems perfect.

I did, however, find a slight amount of oil seepage on the inboard side of the passenger side halfshaft/cv joint. Other than that, I can't find a single blessed thing wrong.

I've heard horror stories of people having a similar issue and spending several thousand dollars to fix the issue and the problem persists (in those instances it was either a broken parking break part or a loose brick in the catalytic converter). And I know, knowing my luck, that it is either a one-off freak occurrence or a $10,000 repair.

Anyone have any idea what is causing these sounds?

If I can get a photo to attach to the post, I'll show the oil seepage image.oil.jpg
 
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Gildan

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I was expecting to hear the sound, take a video and upload it to youtube, then post a link here
could literally be anything, but my first guess is ac compressor, you can take the belt off and see if the noise is gone and go from there.
That was the first thing I tried. The AC was off at the time and even with the belt on, I can't get the vehicle to reproduce the same sounds. I checked the CV joints and everything for looseness and wear and can't figure it out (mainly because this has happened just once), but I will go over all the possibilities again.

At first, when I was backing up, I thought it was a bad CV joint on one side or the other, but I can't find any issues with it. I was driving past a friend's house when the jack hammer sound occurred and he heard it. He's a mechanic and he said he never heard anything like that before. He was even puzzled by the hissing-squealing sound, almost like two rubber parts rubbing together over a leaking air line. But when I say the jack hammer sound was loud, I am not joking that it was as loud a jack hammer from two feet away. It was impressive.

The only thing I can think (and hope) is something got up in the mechanical workings of multiple parts of the vehicle and it was the perfect noise storm. You would think if it was a CV joint issue the clicking/banging noises would continue or would be reproducible, but they are not.

For all I know it was an ABS self diagnostic mode that went wrong (I'll run another level 2 diagnostic on it tomorrow to see if anything went off). But that scraping noise that sounded like a pressure washer spraying the underside of the vehicle is really puzzling - that was ear splitting loud too.

The other possibility is the Stabilitrack system was glitching. I've had the occasional problem if the "Service Stabilitrack System" warning coming up at random a while back that is only cured by shutting the vehicle down for 15 seconds and restarting (I had the dealership go over everything about that warning message and they said it's a common issue that is meaningless. Yeah, right. LOL!).

The problem of getting a video of it is that so far, this is that I can't reproduce the problem even by retracing my footsteps, so to speak, exactly.

What has me puzzled is that if it were a bad CV, the clicking/banging/etc., would not go away. Is it possible that the ABS self diagnostic or the ANS itself glitched along with the Stabilitrack routine?
 

Doubeleive

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check your u joints and driveline that's about the only other thing that makes extremely weird noises, my wifes driveline was making a horrible sound thought it was the transmission but it drove perfectly fine after some testing (driving in different gears, forward/reverse, different speeds etc I finally figured out it was the u-joints, had them replaced and the sound vanished.
 
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Gildan

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check your u joints and driveline that's about the only other thing that makes extremely weird noises, my wifes driveline was making a horrible sound thought it was the transmission but it drove perfectly fine after some testing (driving in different gears, forward/reverse, different speeds etc I finally figured out it was the u-joints, had them replaced and the sound vanished.
I will try that. I did all the obvious checks and found nothing wrong with anything. But I will go over everything again just to see if I missed anything. I'm beginning to suspect some kind of intermittent issue with either the stabilitrack or ABS system. I'll do a computer scan in the morning just for sh*ts and giggles to see if anything there turns up. It is a GMC and 99% of stuff like this is electrical or computer. LOL!
 

swathdiver

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I will try that. I did all the obvious checks and found nothing wrong with anything. But I will go over everything again just to see if I missed anything. I'm beginning to suspect some kind of intermittent issue with either the stabilitrack or ABS system. I'll do a computer scan in the morning just for sh*ts and giggles to see if anything there turns up. It is a GMC and 99% of stuff like this is electrical or computer. LOL!
The only thing that makes noises like that is the ABS pump. Which is on the other side of the car, driver's side. Sound travels.
 

Teamiez

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The one and only time I had a fast paced banging sound under my Tahoe is when the transmission started to take a dump...beated it ******* the thruway and when slowing down on the off ramp that’s when it occurred. Immediately looked under vehicle and everything was 100% fine. After that I noticed the very slightest hesitation when taking off from a stop. Few days later the transmission smoked it’s self after a stop sign. Just my experience lol...
 

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