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Noise from gas tank (metal expansion)

2002 GMC 2500 SLE with extra large gas tank (46 gallon). Makes a banging sound a few minutes after stopping a vehicle and turning off engine. It used to rarely do it an now I hear the sound sometimes when driving down the road. I do have a locking gas cap. At least I think the sound is coming from the gas tank. However I could not rule out catalytic converter or muffler.

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Manage My Life
I don't have the original gas cap. Shortly after I put the tank on way back in 2003, I got a locking gas cap. The tank always made a sound usually after parking and stopping the engine, but it was barely noticeable. Now recently It does it going down the road. So I bought a non locking gas cap to test. I noticed a bang about every half mile driving around our little town. So, my next plan is to drive around a while without a gas cap on and see if the banging is around. I don't think I have exhaust problems, that was inspected recently. I still think I may not have the right gas cap. The tank is a Transfer Flow 46 gallon tank I had installed way back in 2003. It may be i still don't have the correct cap.
by Manage My Life
March 20th, 2012
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bikerbigpapa bikerbigpapa
If you still have the original gas cap swap it back out for a couple of days. There is a safety valve on the cap to prevent excessive vacuum, from the EVAP system, collapsing the tank. The exhaust would be more of a crackling sounds than a banging sound.
by bikerbigpapa bikerbigpapa Earned 42 community points in Automotive
March 20th, 2012
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Manage My Life
Are you getting any check engine lights on dash?
by Manage My Life
March 10th, 2012
Answered in 2 hours
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Joseph Perez
I strange noise coming from the vehicle can really cause some concern and I will be happy to help. I am adding two links below that describe a similar question. I hope this helps while you wait for your expert response.
by Joseph Perez
March 10th, 2012
Answered in 11 minutes
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