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Hello,

I am new to posting on this forum. I typically reference it when reminding myself the usual tools I need to do an oil change, or when I was looking up instructions on how to change the thermostat.

I currently own a 2007 Pontiac Solstice GXP that just hit 90,000 miles today (Pic attached :D). It is a 5 spd manual, no aftermarket mods. I am currently trying to get the car ready to be sold later this year as I am wanting something with back seats.

A little history first: Back in August of 2018, I was in some heavy stop-and-go traffic on an 80 degree (f) day. I had the A/C on at the 2 level with air blowing through the top vents and the feet. When the opportunity presented itself to get back on the highway, I pushed down on that gas pedal and pushed the RPMs to the limit both in first and second gear to get around traffic. Roughly around 15 minutes later, a humming noise began. The humming noise is only present at or above 2500 RPM, regardless of the speed im going. It is heaviest and longest sounding at lower speeds when the RPMs are highest, then the humming is at its quickest, and most repetitive intervals at above 65 mph. Sitting at 60mph causes NO humming. It almost feels like it is coming from the passenger side.

Since this noise has started, I got an alignment done in October of 2018 that did not fix the problem, but it fixed the pulling of the wheel when trying to stop. When the weather here in Ohio got colder, the humming stopped. Now that it has gotten warmer, the humming is back. There is no loss of power, fuel consumption, wheel pulling, or handling. Yesterday, I did an oil change using the same brand of full synthetic (Mobil 1) I have been using since day one of owning it (2014 20,000 miles). I also replaced the spark plugs yesterday. In 2019 so far, I have replaced both front brake pads, calibers and rotors, and in November of last year, the ECT sensor and thermostat.

I have searched the internet consistently to see what this could be and found it could be any of the two things: Something to do with the exhaust or a wheel bearing. My past experience with a wheel bearing (2000 Pontiac Grand Am) was when the humming noise only occurred when making turns, which a few months later developed into a loud cracking noise - entire front end suspension was shot) I am no mechanic, so diagnosing issues is not my strength, but doing the actual work is easy. This car is extremely easy to work on with my tiny hands. I am wondering if anyone has a clue on what I could do to diagnose the issue. I will try and get a video recording of the issue today, should my phone pick up the humming.

I do not trust taking my vehicle to a mechanic as the last time I did for a full synthetic oil change and routine inspection, the mechanic somehow snapped off my Air intake Sensor at the plastic piece that connects to the Air Intake itself. And mechanics around here usually charge $110+ just to look at it. I respect having to charge for an inspection, but the risks are too great. I just took the car in for the recall on the passenger airbag, and the dealership broke something in the seat, now it doesn’t stay up if braking really hard or just simply pulling the seat forward.

Thanks for the advice and assistance!

(PS, if this post shows up twice, I apologize. I posted this a while ago and noticed it did not show up. I tried looking over the Terms of Service to see if there is some sort of delay but couldnt find the information)
 

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Discussion Starter #2
I was able to get the video uploaded here:

https://vimeo.com/322888206

Also, I was in shifted into neutral and let my foot out of the clutch. I was stationary when raising the RPMs, you can kinda here it in this video. I think with it being in neutral, this rules out the wheel bearing being the issue
 

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Just for gins and giggles, try this. It certainly won't hurt anything.

Check the engine shroud where it makes contact at the bottom of the windshield. Look for gaps where it doesn't make flush contact with the glass. If there are gaps - that's a clue.

Take a long strip of back electrical tape and run it along the shroud where it contacts the glass - overlapping the shroud and the glass - making a solid seal.

Take her on the road and see if that solves your humming problem.

It did mine.
 

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As it occurs when the car is stationary, you can easily and immediately rule out anything suspension related, and most of the driveline.

If it was me, I'd remove the accessory belts and start the car. That'll tell you whether to dig further into the engine or one of the belt driven accessories.
 

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Well after some more looking around today before taking off belts, I came across this beauty. I do believe she is the culprit. Looks like it was hanging on by a tiny tiny piece of glue. Looked through the forums and came across an epoxy fix. Went ahead and sealed it up, and now the waiting process begins. I hope that was the cause!

https://drive.google.com/open?id=1OqgH4sh-wDQ0J-xdlV0tf5w_7moWd8UX
 

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I had let the adhesive set for 24 hours and the humming is still present. I decided to do a bit of driving around and noticed that when past the 4500 rpm range, the vibration and humming is practically gone, or if the turbo is doing most of the work. (Like when in 4th gear at 35 mph, accelerating). The humming is gone when the PSI hits around 10-15 range. I hit 95 mph on some back roads today and the humming and vibration was gone. Typically, the vibration is mostly felt in my feet on the floorboard, while some can be felt in the steering wheel. I will move forward with testing out the taking off the accessory belts and starting it.

The humming is less noticeable at higher speeds or if the turbo is being utilized a lot. If the turbo is not being used and the car is going a more consistent speed or the if the RPMs are consistent with no stress on the turbo, thats when the humming is the loudest and most felt in the floorboard and steering wheel.
 

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Discussion Starter #10
The serpentine belt diagnostic didnt work. I took it to two different mechanics, (made sure I could watch) and I have two telling me different things

1)Regardless if the PCV hose was reattached or not, its still the culprit of the humming and vibration
2) An internal component of the turbocharger is either warped or damaged. The warmer air is making the turbo worker harder, thus the increase in volume. The turbo is also making the exhaust system shake under the car.

Before I start buying parts, is there a fuse that I can disconnect that will disable the turbo so I can test out the hums?
 

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The turbo is mechanically driven by the exhaust gas, so not really.

But you can remove the intake tube going to it (the part that you just epoxied) and you should be able to visually inspect the compressor wheel. A few drops of oil is normal. If there isn't any scoring of the walls reach in with a few fingers and give the end of it a wiggle. It should spin freely and have very little play.
 

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I replaced the Turbo and outlet duct last month and its still doing it. I just now had time to go to another mechanic and they found the following notations:

Lower Cat Converter Bracket - needs replaced
1 bolt broken - 10m x 1.5 x 30
Upper heat shield - manifold and turbo broken
Metal too thin to repair

Then listed parts:
Lower converter base/support
Turbo heat shield upper 1
Turbo heat shield upper 2

I checked with 2 dealerships and i cannot get a definitive answer to these part numbers. Anyone know what to sesrch for so i can find these through GM parts online?
 

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I replaced the Turbo and outlet duct last month and its still doing it. I just now had time to go to another mechanic and they found the following notations:

Lower Cat Converter Bracket - needs replaced
1 bolt broken - 10m x 1.5 x 30
Upper heat shield - manifold and turbo broken
Metal too thin to repair

Then listed parts:
Lower converter base/support
Turbo heat shield upper 1
Turbo heat shield upper 2

I checked with 2 dealerships and i cannot get a definitive answer to these part numbers. Anyone know what to sesrch for so i can find these through GM parts online?

I'm not sure what they even mean by Turbo heat shield upper 1 & 2. There's just one piece of the heat shield. See #5 here: https://www.cultragfactoryparts.com/auto-parts/2008/pontiac/solstice/gxp-trim/2-0l-l4-gas-engine/engine-cat/turbocharger-and-components-scat

Also not sure what they mean by Lower converter base/support? Look-see here: https://www.cultragfactoryparts.com/auto-parts/2008/pontiac/solstice/gxp-trim/2-0l-l4-gas-engine/exhaust-system-cat/exhaust-components-scat

I will add that your videos make it seem like resonance. I would've gone with accessory belts too first off, but if not those, then try having someone rev the car while you press (with a piece of wood) on the turbo heat shield. If that's loose. if could well be resonating. If that fails, use a jack and block of wood to put some gentle pressure on the exhaust by the cat, and see if that stops it.
 
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