96 Pathfinder: Strange humming sound from gas tank when ignition off?

[ponga]

Grettings! I'm hoping someone would have an idea here at to why under certain conditions, strange humming sounds can be heard from the gas tank area of my 96 Pathfinder. Any suggestions are appreciated!

The humming sound, sounds like a hydrolic sound, as in fluid under pressure moving through tubing or pipes. I've noticed this when I drive my Pathfinder to the mountains (increase in elevation), turn off the engine and get out.

Last time, after turning off the engine and with the key completely removed, and the sound was present, I removed the gas cap and boy howdy! There was some serious pressure in the gas tank as gas fumes came pouring out first with some pretty good pressure and even after a minute or so, there was still venting going one.

My buddy suggested that perhaps the vent on the gas tank is clogged. Makes sense. But having never run into this, I figured I would bounce it off of you guys. Any ideas??

-As maybe a related item, my Pathfinder is throwing a "Rich condition" code, but that may be related O2 sensor fault code that it's throwing or not. Maybe not related, but I wanted to mention it.

Thanks!!! -ponga

[Fisherdude]

I have the same noise coming from my 96 pathy, but it hasn't affected me yet so I don't give a crap.