My fuel tanks build pressure, you probably have a vacuum relief built into your cap. My tanks builds enough pressure to give a pretty good pressure burst when I open the cap. It used to leak from the sending unit. I found that the sending unit o-ring was not even in place. It seems that my wife had tanken the car to Nissan for a recall due to some type of fuel pump problem. WEll it seems nissan created a new problem with fuel leaking.
You may very well have a sending unit gasket problem that needs to be tended to.