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Discussion Starter #1
I have a couple of sounds occurring with my car that I haven't seen posted about by others. I posted about one of those sounds a couple months ago...(see my post about a "warning buzzer") Since then, I haven't heard that particular sound at all. However, since then I have experienced 2 new sounds which I hear intermittently. Because they are intermittent, I probably won't be successful in recording them. Even if I was, it would be difficult for a recorder to pick them up.

The first sound sounds like a loose screw or nut rolling in the upper body area of the car, in the upper window area on the drivers side. I notice it sometimes when coming to a quick stop, or when accelerating. It sounds like the part rolls and then becomes lodged at the end of its roll. The sound doesn't come back until the part eventually dislodges itself, and then rolls from either the front to the back, or vice versa. I did have my door lock receiver replaced awhile ago...could the loose part be a result of that repair?

The second noise is more worrisome to me, and I have so far only noticed it when using the ICE. I get a "thunk" or "clunk" sound coming from the right rear of the car when accelerating from a stop, most often between 15-20 mph. Recently I was on the highway in stop and go traffic, and the sound was happening fairly consistently. I pointed it out to my wife, and she heard it too. I am quite sure it isn't anything rolling around in my trunk. I was wondering if the sound could be transmission related, but so far I haven't heard it when using the car in electric mode (no ICE).

I would like to take it in to the dealer, but I don't want to waste a trip and have them tell me they couldn't hear the noise. So, I've been waiting for both sounds to become more noticeable. Maybe I'll be able to record the sounds at that point.

Any ideas what could be going on with any of these sounds?
 

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IIRC, the muffler is located on the right in the Gen2. Maybe a muffler hanger strap is not connected properly. I think that that would be easy to diagnose and repair. If you lie down on your back and tried to move the muffler by grabbing hold of the tailpipe and push-pulling, you would soon discover if that is the problem. Properly mounted the muffler should not move, except under great force from you. I believe that there is a rubber connector holding the muffler stationary to the car body. It might be missing or it might not be connected to either the body or to the muffler. I doubt that the transmission has anything to do with the noise. Good luck.
 

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The sound coming from the rear wouldn't be the infamous "chuggle" would it? There are some youtube videos demonstrating it as well as a number of posts on the issue which apparently is "perfectly normal".
 

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The second noise is more worrisome to me, and I have so far only noticed it when using the ICE. I get a "thunk" or "clunk" sound coming from the right rear of the car when accelerating from a stop, most often between 15-20 mph. Recently I was on the highway in stop and go traffic, and the sound was happening fairly consistently.
This is not the "chuggle" but a new problem that only a few 2016/2017 Volt owners have. See following threads for more info, especially the first one which has a link to gopro video of the sound:

http://gm-volt.com/forum/showthread.php?252514-Bang-Click-noise-coming-from-rear-passenger-side-2016-Chevy-Volt
http://gm-volt.com/forum/showthread.php?261057-16-Volt-backfiring
http://gm-volt.com/forum/showthread.php?227073-Clank-noise-when-on-ICE-and-making-right-turn
http://gm-volt.com/forum/showthread.php?282465-Sporadic-clank-sound-coming-from-rear-when-ICE-kicks-in-sometimes-(25-of-the-time).

The fact that on the highway you hear it more frequently, were you driving for at least 15 minutes? If that's the case, you probably got your coolant up to temp (~190F+) and with ambient at about 60F+, you will get these bang/afterfire sounds. Happens for me in both HOLD mode (Charge Sustaining or CS) and when I run out of EV range (Charge Depleted or CD mode).

So far, dealers have said it's normal and there's nothing to fix. >_<

My local dealer did a great job troubleshooting the issue but didn't find any loose parts. The tech even used things called "chassis ears" and isolated the loudest point as being at the rear of the exhaust. Below are my own vids documenting the issue:

https://vimeo.com/228493984
https://vimeo.com/228494160

If you're really worried, I'd take it up with the dealer and have them add to the number of complaints back at GM regarding this issue. Perhaps then it will lead to actual troubleshooting from GM engineers. Literally the service advisor from my dealership relayed to me that GM engineers said "some Volts make the sound, some don't" and that the sound was "normal". A minority of users to me doesn't sound like normal.

I have since started complaining to my state Consumer Protection office. Not sure if I can qualify for a lemon law replacement (I love the Volt, don't want to sell it back, want it replaced!), but hopefully some official letterhead/email can help convince some person with authority at GM to release some funds so an engineer can properly diagnose and fix the issue.
 

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Discussion Starter #5
Thanks quirkySquirt, This is the exact thing I was talking about. I guess my search terms weren't good enough because I was looking for posts such as the ones that you referenced but didn't find them. From inside the cabin of my car, my sound is not as metallic...it is a duller sound; but I think it is the same sound that others are experiencing. I have never heard it unless I was using the ICE, and it is coming from the right rear of the car. It was more noticeable when I was on the highway while doing a lot of stopping and starting. I had driven my car for over 15 minutes, and temperature outside was in the upper 70's.

I did look under the car yesterday and my muffler is pretty solid, everything looks like it should. I don't think the sound is caused by movement of the muffler. I do think it is a backfire issue.

So now, what should I do? Sounds like from reading the posts that there isn't a solid diagnosis or fix at this point. My dealer is about an hour away. I will definitely bring it to their attention, but it probably won't be until I'm due for the next tire rotation in about 7K miles from now. At least I will be able to reference these posts to the dealer to explain what I'm noticing!
 

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No ill will, fintonissimo, but hearing you have the problem brings me some hope. Adding your complaint *hopefully* convinces GM to start investigating this and at least notifying customers that they're working on it and that it is not in fact "normal".

I too have the bang sounds on the highways when in traffic. If you ever do bring it in for the afterfire issue, maybe recommend to your tech to utilize "chassis ears" to isolate the sound. Hopefully, it's in the rear of the exhaust like mine.

EDIT: If you want, you can also ask GMC customer service using following contact page:

http://www.gmc.com/contact-us/chat.html

I was going to go that route first but already started an informal complaint process through my state's consumer protection group (not lemon law yet, just informal). Process is supposed to take a 2-3 weeks so I'll hold off contacting GM.
 

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Discussion Starter #7
Well, I finally brought my car in yesterday to the dealer for a tire rotation and to see if they would be able to fix some of the other things mentioned earlier by me in this thread. The tech said that he was unable to duplicate the after fire bang, but assured me that he believed that I was telling the truth. He said that GM has indicated that a fix for this will be available sometime in the 2nd quarter of 2018, and that they will let me know when I can bring in the car for the fix! The funny thing is that as soon as I pulled out of the dealership, the after fire bang occurred! I turned right around and went back to the dealer, got the tech to ride with me, and fortunately, he also heard the sound. So, I feel a victory with that! In addition, I had them fix a squeaky panel on the driver's side door. They found a loose clip and reattached it for me. They were unsuccessful in locating the source of my other rattle, (the one I sometimes hear that sounds like a loose part rolling around) so there was no fix for that, unfortunately. I complained about the lack of heat coming from the heater, and they reprogrammed my HVAC system control. So all in all, it was a pretty successful visit! I am very hopeful knowing that a potential fix for the after fire bang is most likely coming soon!
 

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Discussion Starter #8 (Edited)
Got the bang/clunk fixed today, the fix (program power inverter per bulletin 18-na-174) is now available!! Hurray!! My other rattle still exists, though. They haven't been able to hear the loose part rolling around, or figure where it could be to fix it.
 

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Got the bang/clunk fixed today, the fix (program power inverter per bulletin 18-na-174) is now available!! Hurray!! My other rattle still exists, though. They haven't been able to hear the loose part rolling around, or figure where it could be to fix it.
Wow this is good news. I have the same issue. Did GM contact you for the fix? Mine is a 2018 with 2500 miles only and just started to have this bang/clunking/click noise. Should I just go to the dealer and mention this bulletin to fix it?
 
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