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Discussion Starter #1
I 've had my 2011 for nearly 3 years and I know this sound is normal, but never really cared what it was until now. Usually within the first few minutes of my morning drive, there is a sound, sometimes two or three times which sounds as if you ran over a piece of rubber and it hits the wheel well. I always figured it may be something to do with the gas tank pressurization. Kind of like a low pitched thump or thud type noise. Pretty distinct noise, I'm sure any gen 1 owner will know the sound.
Anyway, what is it for sure???
 

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Common reoccurring noise for many in the Gen1 Volt. Most likely what you are experiencing is from the rear spoiler. The plastic of the spoiler is extremely close to the body of the car where it is attached.

With the thermal expansion coefficient for the plastic being different than the metal hatch, there is a point at which the contact between the two materials causes a slip, which generates the loud thud/pop noise.

I remember the first time I heard it, I thought my rear window had cracked! There is an older thread that mentioned a fix, I believe it involved the dealer removing the plastic panel on the hatch and tightening the mounting screw on the spoiler. Never taken the time to try to remove the cover to find out.
 

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My gen 1 made a thumping noise when I first got it, but only over certain bumps. Adjusting the little rubber stops under the hatch did the trick, took some trial and error.
 

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Discussion Starter #4
I suppose it could be what PH2 said. I never in a million years would have guessed that, so I am not positive that is where the noise is coming from. I know it is not bump related or anything like that. It usually occurs within the first half mile of driving. And if you have ever run over a small piece of rubber such as from a tire and it bounces off the inner wheel well, that is exactly what it sounds like. And I am positive that is not the cause. It is too "regular" of a noise to be something I run over. Sounds like it is coming from the right rear of the car. I will look at the spoiler as PH2 mentioned, but even if that is the cause, I assume it would not be something you would be able to notice just by looking at it. Anyway, keep the ideas coming. THANKS
 

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Yep, always on the right rear of mine too. Sometimes if the temperature is right, I can get it to pop with a little pressure, maybe you can test yours that way. I've also had it happen in a car wash on a hot day... guess the water cooled it down enough.
 

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I suppose it could be what PH2 said. I never in a million years would have guessed that, so I am not positive that is where the noise is coming from. I know it is not bump related or anything like that. It usually occurs within the first half mile of driving. And if you have ever run over a small piece of rubber such as from a tire and it bounces off the inner wheel well, that is exactly what it sounds like. And I am positive that is not the cause. It is too "regular" of a noise to be something I run over. Sounds like it is coming from the right rear of the car. I will look at the spoiler as PH2 mentioned, but even if that is the cause, I assume it would not be something you would be able to notice just by looking at it. Anyway, keep the ideas coming. THANKS
The spoiler expanse sound is a "pop" sound like an acorn hit the back of the car. The gas tank pressurization system (in the right rear) is a more rhythmic sound, like a small buzzing/banging sound.
 

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The spoiler expanse sound is a "pop" sound like an acorn hit the back of the car. The gas tank pressurization system (in the right rear) is a more rhythmic sound, like a small buzzing/banging sound.
I have had my 2014 for about 5 months. I have heard the "acorn" a couple of times. That is exactly what it sounds like.

2014 Volt Premium - Safety pkg 1 and 2, Navigation
 

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The spoiler expanse sound is a "pop" sound like an acorn hit the back of the car. The gas tank pressurization system (in the right rear) is a more rhythmic sound, like a small buzzing/banging sound.
I would have concern for any compressor making a banging sound. I've heard the Volt's fuel tank compressor many times and would never describe it as a 'bang', always a hum/buz (like a small tire compressor but muffled). I've also only ever heard it from the outside of the vehicle, but I suppose that varies with volume inside the cabin.
 

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Did you leave you mother-in-law in the back?
 

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Discussion Starter #11
I can agree the sound being like an acorn hitting the back of the car. I couldn't initially use that analogy as there are not many acorns in Phoenix. A bit hot for those. Anyway, the car is parked in the garage every night so there may be a big temperature difference (hotter or colder) between the garage and the outside, so the thermal expansion theory would make some sense. As I said, it usually happens within a 1/4 mile of driving, but sometimes I go a mile or two before I hear it. So unless anyone has other ideas, I am going to agree with PH2 and assume it is the spoiler. THANKS
 

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Funny..I was going to post about this exact thing today. Ours is sometimes rather loud like a tennisball hitting the back of the car. Other times ..yup...acorn hitting it. I dont think its the expansion thing. I experience it daily...first drive, 2nd 3rd, no matter...happens like clockwork about 1/8th of a mile into a drive. No matter if sitting outside in the sun before, in a garage, raining, etc....always happens.
Strange.
 

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I hear this 'acorn' way too often. Is it normal to hear this almost every day?
Depends. Is the car experiencing enough if an external temperature change between night and day to force the spoiler's expansion/contraction? Perhaps your spoiler attachments are over-tightened, causing too much resistance to expansion movement, or maybe there is some dust/grit buildup interfering with the "sliding" action. Some dealers have removed the spoiler, cleaned, installed slip tape and snugged the attachment just enough but not too much.
 

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I'd Be willing to bet good money that I can remove my spoiler and it will still make the same noise daily.
Seems like a good test to possibly eliminate one potential cause. Let us know how it goes.
 

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There are huge temperature differences here in California (especially inland). So I guess that explains it.
 
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