Hey guys. Got a strange question. When my truck is just sitting there idling or running around with the windows down, it lets out a farting noise from the fuel cap. The tank is obviously becoming pressurized somehow. I've tried new caps so thats not the issue. When i go to fill it up and pull the cap off a big rush of air comes out the neck. Somehow i gotta unclog the vent system or whatever that allows pressure to not build up in the tank. Any ideas or ways to troubleshoot it?