Hey guys, sorry I haven't updated this thread in a while. I drove the my 108 this past week and replicated the noise issue. And, the second I opened the gas cap, the noise would stop! So it's definitely pressure building in the gas tank.

Jose

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1972 280SE 4.5 Dark Green, Cognac. Pics!
2014 Range Rover Sport Supercharged. Santorini Black, Dynamic Package, Front Climate Comfort and Visibility Package, Vision and Convenience Package.

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2010 Explorer Limited, 2010 R350 4MATIC, 2011 Jeep Grand Cherokee Overland, 2009 Audi A4 Cabriolet, 2009 Ford Flex, 2008 Mercedes-Benz ML350, 2008 Mercedes-Benz E350, 2007 Mercedes-Benz C230, 2005 BMW X5.