just need to ask...

IMO, Usually your gas tank will "pshh". It is more likely to do so after its been running. Means your gas cap/tank is holding pressure. I may be wrong, but that is my take on it.

Yup. There's a minimal amount of pressure in the tank.

Some cars are actually able to detect the lack of pressure (read: You left your gas cap off) and can throw a code.

Don't worry, a little bit isn't at all un-common.

If you've been heating the tank due to a malfunctioning exhaust or something... expect a lot more than a brief "PSSHHH" to come out.

it makes me happy to know that that is normal and actually a good thing, i just had to replace my fuel pump and before my car never made that noise, after i got done i drove it around a bit and then put gas in it and it did it and made me worried, but now i know thats good so no worries, its odd too because the previous owner replaced the fuel pump before i bought it, but i dont think he did it right as far as having the tank sealed right, and i also dont think he changed the strainer or fuel filter when he changed it which basically ruined it, i didnt make that mistake and now my car runs like a champ