every once in a while when i shut the truck off i hear a boiling of "glug glug" noise. Today i noticed it sounded like it came from the rear of the truck. it dawned on me that it might be fuel pressure building in the tank from a bad charcoal canister. When i fuel the truck i get some wosh of pressure but nothing crazy or fuel poring out like some people describe with a bad canister. Any ideas? It does not bother me much. I might just let it ride unless it is something simple like a charcoal canister.