Gas cap not venting
 

Got an 08 T&C 3.5l. Every time I go to remove the gas cap it's like breaking a vacuum seal and you hear a suction sound. Any ides why it's doing this

Did you review your gas cap? for any broken seal? any failure message on ECM?

Its meant to do that. Gas tanks no longer vent to the atmosphere as part of the emissions system. Vapours that once escaped are now captured by your carbon canister located under the vehicle, this then passes them to the engine where they are burnt off.

Thats a very basic description but basically its meant to reduce pollution!