radiator cap question

[VtekII]

hey guys im just curious... i noticed today on my 04 when i twist off the cap on the radiator right about the last 1/4 turn i can hear it either suk air in our push it out. im not really sure which one it is but i can definitly here air move. is this normal or is my cap going bad? or something else an issue?

to me it would seem coolant would have to be dissapearing to create an air vacuum in there, but from what i can tell the coolant level stays the same all the time?

 

[945LSTANG]

pretty sure thats just the normal sound it makes as it depressurizes the cooling system.

 

[VtekII]

hehe ok im just paranoid like a crack head about this car... i just piiked it up a little over a month ago. i havent been able to drive it more than maybe 30 miles. so every little noise or smell i find i get all