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My wife came in from the garage and said there was noise coming from the rear of my baby. Sure enough there was a loud whirring/buzzing noise that seemed to be coming from the middle of the cargo area.

Now, besides the battery, I know there isn't much below the cargo hatch.

Looking under the car, the noise was coming from the center, by the axle. There's a bunch of components, tubes and wires there, some of it attached to the gas tank/fill port.

I opened the driver's door and hit the gas fuel door button. The noise stopped. Obviously the gas tank pressurization system had gotten stuck for some reason. I opened the gas fuel door, the gas cap was tight. I closed the fuel door, the noise did not come back.

I had washed the car earlier (including the gas fill port), and suspect the pressurization system got confused somehow after I closed the port door and started pumping away. The pressurization process should only take a few moments from my experience, not minutes. I can't imagine just wiping the cap and splash area with a towel could have loosened the cap, though I suppose anything is possible.

Anyway, if you hear a loud whirring/buzzing back there, try pressing the gas fuel door button on the driver's door to see if it stops. Open the gas fuel door, check the gas cap, close the door.

gas tank pressurization.jpg
 

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Nice post and picture. Just to be clear ... you released the gas port door and depressurized the system but then did not unscrew the gas cap. You then just closed the gas port door and then the system was seemingly confused? How long would you say you had the gas port door open? I think there is a time limit for unscrewing the cap as I recall from the manual.
 

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I did not unscrew the gas cap, Scott. I simply made sure it was still snug (it was). Then I closed the door.

The system was "confused" (my technical explanation, haha) BEFORE I did that. It had started pressurizing after I had earlier opened and closed the fuel door, and had apparently just kept going until I came out and hit the gas door button.

So at no time did I actually open the gas cap (at least not intentionally). It's improbable that wiping the gas cap would have enough force to open it, especially given it was tight when I did my "fix" and inspection afterwards. For some reason the car thought the tank needed more pressure. Like the "More Cowbells" SNL skit, I guess it just could not get enough :)
 

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There is occasionally a noise from that area when parked. I've been told its the car doing some sort of diagnostic and it's nothing to worry about. While it may be related to the gas pressurization system, I don't think it is stuck as suggested here.
 

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I did not unscrew the gas cap, Scott. I simply made sure it was still snug (it was). Then I closed the door.
Yes, that is exactly what I thought (and attempted to write) ... that is why I thought it may have caused it to be confused. In other words, just a non-typical set of events. Although I could see where their Quality folks would have tried that one.
 

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In other words, just a non-typical set of events.
It's pretty typical for me to open that door and clean the area with a damp towel. To my knowledge, this noise has never occurred in the 8 months I have been doing it. Nor have I ever heard that racket before. I've heard gurgles and pumps and such from the front of course.

I'm chalking it up as a one-off "weird things sometimes happen" event. Like the day that OnStar said my car was no where on the planet (the system could not locate me, nor could I download maps).
 

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My volt was doing this very thing, yesterday. I noticed it while walking through the garage to go outside. It was a buzzing noise coming from the rear of the car (sounded like it was coming from the rear bumper area). I do not know how long it was on prior to me noticing it but it did last for 2-3 minutes after and then shut off.

I, too, thought it might be the fuel pressurization system. I had NOT opened the gas fuel door or pressed the gas door release button prior to this. In fact, I have not filled my Volt with fuel, ever.

Could the gas tank lose pressure, over time, and need to re-pressurize on occasion?
 

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Identical observations to that of SDVolt. Noticed it within a month of leasing. And 2 weeks ago while I was reprogramming my delayed charge schedule. Don't think that caused it.


Took a video of it until it stopped (2+ minutes). The sound got louder as I approached the rear-right side (where the gas tank cap is).
 

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I believe it's part of the diagnostics running on the fuel evaporation leakage system. My Pruis does the same thing.
 

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It's pretty typical for me to open that door and clean the area with a damp towel. To my knowledge, this noise has never occurred in the 8 months I have been doing it. Nor have I ever heard that racket before. I've heard gurgles and pumps and such from the front of course.

I'm chalking it up as a one-off "weird things sometimes happen" event. Like the day that OnStar said my car was no where on the planet (the system could not locate me, nor could I download maps).
I don't know, Steve. In the Volt you may as well be on another planet... that's how good I feel whenever I get in one!
Cheers, and to all, happy new year!!!
 

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Noticed the whirring sound emanating from the right rear of the vehicle tonight while plugged into 240v charger in delayed charge mode. Loudest when listening under right rear wheel area. Went inside, checked my Onstar mobile app and everything appeared normal. Went back to car to consider unplugging, and the noise had stopped. Would be nice if a Volt advisor could explain what exactly is occurring when this noise happens. Would help if we all knew this is a normal phenomenon with the Volt, and WHAT exactly is being tested when this happens. Maybe a Volt advisor is reading this stuff...
 

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I have heard the noise a month ago or so on our 2012 Volt. Didn't know what it was. Came back about 10 minutes later and the noise had stopped. Since then, I found this thread and have listened for the noise. Last night it happened again. This time, armed with some info from this forum, I pressed the gas door release button on the driver door. The noise instantly stopped. I closed the gas door without touching the gas cap. The noise did not return.
Both times, the car was connected to 110 VAC charger, but not actively charging. I have never opened the gas door before, as we are still driving on the dealer gas.
Have no idea if this happens every night, once a week, or whatever. Just happened to catch it those two times while taking the trash out to the garage.
Would be reassuring to know if this is normal.

Bruce
 

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I work for GM as a powertrain diagnostic engineer. What you are hearing the car checking the integerity of the fuel storage system. 3 to 5 hours after the engine and car shuts down it runs a vacuum pump to determine if there is a leak in the fuel storage system. You do not hear the pump everytime you shut down the car because there is a minimum time between tests, minimum engine run time, ambient temperature limits, and numerous other criteria that have to be met prior to the test running. On other vehicles the Evaporative diagnostic test is refered to as the loose gas cap light test because a loose gas cap used to be the cause of almost all of the failures. So now GM flashes a message to the driver to check his gas cap prior to turning on the check engine light. Saving the owner a service charge from the dealer. GM does not pay the dealer under warrenty if the failure was caused by the owner, that is the gas cap was loose.
 

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Just went into the garage and experienced this noise as well. Was getting kind of concerned as it sounded a bit un-natural (totally unlike the soft whirring of the cooling fan when charging). When it quit, I came here to see if anyone else had experienced this and sure enough... By the way GM, shouldn't this noise be added to the list of known noises? That was the first place I checked and there was no mention of this noise.
 
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