2007 Chevy Cobalt Thumping

Tiny
JFURLOW
  • MEMBER
  • 2007 CHEVROLET COBALT
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 25,000 MILES
Within 10 minutes of starting my car and driving for a while (always after the car has been sitting for at least a couple of hours) there is a thumping coming from the back right side of the car (4-5 thumps). It has happened both while I am driving and while stopped at a stoplight/stop sign and during summer and winter. The antenna is tight so we have ruled that out. We have even tightened it to make sure. Definitely not the tires too. Almost sounds like it's coming from the trunk or as if someone is knocking on it from the outside. The car is in good shape and the thumping does not seem to affect anything while it happens. My gas mileage is right where it should be (25-30 miles to the gallong) so it does not appear to be affecting that either.

I'm more concerned with making sure it isn't hurting anything in my car. Doesn't bother me other than I can't figure out what would be causing it and neither can friends of mine who have decent knowledge of cars.
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Wednesday, August 12th, 2009 AT 11:45 AM

4 Replies

Tiny
DOCFIXIT
  • EXPERT
Wonder if it is the fuel tank? Something to do with Evaporation system ie. pressure in tank. Any trouble filling tank or lots of air escape when cap loosened?
See diagram


https://www.2carpros.com/forum/automotive_pictures/198357_Graphic_50.jpg

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Wednesday, August 12th, 2009 AT 2:38 PM
Tiny
JFURLOW
  • MEMBER
No problems filling the tank. I don't recall an excess of air when I open it either but that would definitely be the area where the noise is coming from. Have you heard of this before and do you know of anything specific I can check? If it's just going to be an annoyance I'm not worried about it. But I certainly don't want to ignore it and have it be something serious.
Thanks!
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Wednesday, August 12th, 2009 AT 8:55 PM
Tiny
DOCFIXIT
  • EXPERT
I would take into Dealer and get on record the problem just for insurance in case it becomes a problem. And they may have run across your thump before.
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Thursday, August 13th, 2009 AT 8:20 AM
Tiny
JFURLOW
  • MEMBER
Might end up doing that. Trying to get advice first before I blow the money on a diagnostic.
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Sunday, August 16th, 2009 AT 4:46 PM

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