I have a mystery sound that I'd love to hear some opinions on: We went camping this weekend in N. Ga. in my 1990 FJ62. 275K miles, h55f, I have the 38 gallon tank that MAF sells for the FJ62. Installed by ACC in Atlanta. It's been on the truck about a year. We filled up about 4:30PM at a gas station outside Dahlonega, Ga. I didn't fill it all the way up because it has been known to push gas out a vent line when its hot and off camber. Pulled out of the gas station with about 7/8 of a tank. Temps were mild 60-70 degrees when we stopped and dropped to the 50's by morning. FS Roads were plenty bumpy. Lots of bumps, hills, etc... We hit camp about 5:30. After we stopped and set up camp we noticed the noise coming from the tank. It was like it was bubbling or burping. The noise was audible 30-40 feet from the truck. It was intermittent, but continued all night long. It was still doing it when we packed up at 11:00 the next morning. I tried taking the cap off to see if there was pressure building up or a venting problem. No hiss when I loosened the cap. No change in sounds with it on or off. We have camped in the truck a few times in the last few months and never noticed this. The truck ran fine after the fill up, and I have burned through 10-25 gallons of it since we camped. No problems. Thoughts?